The Staffel Invisible

By Donald E. Keyhoe

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CHAPTER I. THE BOCHE FROM NOWHERE.
CHAPTER II. DEAD MAN'S MASQUERADE.
CHAPTER III. DEVIL'S DROME
CHAPTER IV. INVISIBLE DOOM

Etext from pulpgen.com

CHAPTER I. THE BOCHE FROM NOWHERE.

FOR THE THIRD time since taking off from his Vosges canyon hideout, Captain Philip Strange chuckled to himself. “Be ready for role as Second Lieutenant Archie

Bye, unobtrusive, mousy character,” the wireless code from Colonel Jordan had said. Strange wedged the control stick between his long legs and took out his makeup kit. A timid, pink-cheeked face looked back at him from the mirror, its only claim to obtrusiveness a wispy yellow mustache which struggled feebly on his upper lip. The G-2 ace grinned at his carefully made-up features.

“Well, Archie, I hope you're 'mousy' enough to suit the Colonel. Wonder what he wants of a goofy bird like you?”

Archie smiled back apologetically from the glass. Strange then replaced the kit in his flying- coat and glanced over the cowl of the Spad. The field at Rondecourt lay ten miles ahead, with the Meuse River shining in the rays of the setting sun. He sent the fighter moaning down in a long power glide, his mind on the full message from the G-2 chief:

“Meet me at office 365th Observation, Rondecourt, soon as possible. Be ready for role as Second Lieutenant Archie Bye, unobtrusive, mousy character, reporting from G.H.Q. with routine dispatches—I. J.“

Strange sobered as Rondecourt drew nearer. It was the headquarters for Fifth Corps, and he might run into old friends there, as he had on other missions since his death was officially announced. It was always difficult, after those lonely weeks in the Vosges, to keep from letting them know he was still alive. But he had told only the few whose aid had been required.

It was more than two months now since German spies had invaded his secret quarters in Chaumont, killed a dozen G-2 pilots assembled there, and left him for dead. To avoid further slaughter of Intelligence pilots because of German hatred for him, he had persuaded Colonel Jordan to go through with a false burial while he himself disappeared.

Later, with Jordan's help, he had established a secret base in a Vosges canyon, carrying on with such missions as the G-2 chief ordered. A Chinese cook and an Army Air Service sergeant were his only regular companions at the cavern, and it was with relief and a keen anticipation that he had received Jordan's summons to Rondecourt.

From the tone of the message, the affair seemed not too serious. Jordan would probably have called for one of his already-established roles—such as Tex Kane, the flying cowboy, or Colonel Smythe, British Brass Hat—if there had been more to it.

Then abruptly a glimpse of wings against the sun broke in sharply on his thoughts. He shaded his eyes, relaxed when he saw it was only a D.H. Another two-seater now came twisting into the wind for a landing, and he surmised that they had been on an observation mission together. He was starting to circle, giving the D.H.'s the right-ofway, when to his surprise the observer in the nearer ship jumped to his feet, frantically snatched at his gun tourelle, and sent a burst of tracer smoking from his Lewises.

Strange spun around in his seat, expecting to see a Boche diving on the two-seater's tail.

But there was not a ship in sight!

THE G-2 ACE'S eyes jerked back to the observer. The man was firing madly, swerving his guns to right and left, up and down, while the pilot plunged the D.H. toward the field beside the river. Suddenly the observer stiffened, and the spade-grip fell from his grasp. He clawed wildly at the air for an instant, then crumpled over his guns.

The pilot stared back, his face white with terror. Abruptly, part of the left flipper tore off, and bits of fabric flew from the turtleback. The pilot flung his crippled plane into a steep forward slip, his blanched face still staring back over the tail. But then, as though by some horrible magic, that ashen face sudden crimsoned into a dreadful blood mask. The pilot's body tumbled down into the cockpit, and with Liberty wide open the D.H. pitched to the ground. It struck head-on and instantly burst into flames.

Strange swept the stick to his belt and zoomed with his thumb on the trips. Again, his tense gaze raced about the sky. But there was nothing to be seen. Not even a cloud to hide an enemy ship!

The second D.H. had pulled up, and both pilot and observer were fearfully searching the heavens. Strange ruddered in toward the two-seater, then kicked away in consternation. A tiny, weird red blur had appeared in midair, three hundred feet away, and simultaneously the Spad's tail shook under a vicious pounding.

Amazed, Strange saw four more of the tiny blurs appear, flickering, dancing across the sky. Hardly had they materialized before they were gone, to be replaced by still more of the queer red flashes, as though a dozen miniature shells were bursting in quick succession.

Another savage pounding shook the Spad, and fabric ripped from the secret agent's left wingtip. Strange zoomed into a chandelle, eyes slitted behind his goggles. There had to be a ship somewhere—perhaps hidden against the sun. . . .

Directly ahead, two more eerie red blurs appeared, like fireflies dancing across his path. Something lanced over his cowl, and splinters flew from a strut. With a muttered oath, he tripped the Vickers and stabbed a burst toward the blur on his right. It vanished—but two more weird blurs whirled in on the left, and a line of sinister holes streaked across his wing.

Something like an icy hand seemed to close around the heart of Philip Strange. Human foes he could fight, even against odds—but these deadly red fireflies . . .

Wings swam across his sights as he whirled in a lightning turn. He clamped his trips together, but let up on them swiftly. It was the other D.H., twisting frenziedly, with its tail surfaces almost in tatters, and its rear-guns blazing into space.

With a wild turn, the D.H. pilot kicked away from the darting red blurs and dived into the glare of the sun. Three of the fireflies whirled after it, vanishing for a moment, reappearing hundreds of feet away. Strange fought back a desperate urge to flee, and pitched the Spad after the dancing red spots. The guns were thrashing on his cowl, belts half-empty, but he held the trips hard against the stick. If he could hit one of those damned things, he might learn the answer. But the fireflies moved too swiftly.

A groan came to his lips as he saw the D.H. plunge into a spin. But the next instant stark amazement drove all thought of the doomed men from his mind. In a split-second, one of the tiny red blurs spread into a large, dazzling ball of flame, and from out of that ball pitched the figure of a man!

STRANGE had a glimpse of a gray German uniform, of a tortured face as the man beat madly at his blazing hair. Then his tumbling figure dropped into the Meuse, a hundred feet from shore. The ball of flame whirled down a moment later, striking the surface farther out from the bank, and a huge cloud of steam arose, hiding the scene. Strange leveled off, glanced upward.

The fireflies had disappeared.

The second D.H. was now a twisted mass of wreckage in the middle of the field, and a crash- truck was racing out toward it, followed by a crowd of men and officers. Another group was dashing toward the bank, near the spot where the German had fallen.

Strange landed, let the Spad roll toward the line, and the ship had barely stopped when he saw the chunky figure of Colonel Ira Jordan hurrying toward him. The G-2 chief was followed by a potbellied little officer whom Strange recognized as Major Simon Blunk, Intelligence officer for 5th Corps.

Jordan shot a quick look at the number on the Spad, wheeled and gestured for Blunk to wait, out of earshot. He reached the ship just as Strange climbed out. For a second, he looked uncertainly at the G-2 ace's made-up features.

“It's all right, colonel,” Strange said grimly. “This is your 'mousy' character.”

“Strange!” Jordan said tensely. “What in Heaven's name were those things?”

“I don't know,” muttered Strange. “If anybody else had told me about it, I'd never have believed it. I suppose this is why you sent for me?”

Jordan's bulldog face was pale as he answered.

“Yes—but I never dreamed it would happen here at Rondecourt. It's a miracle you're alive.”

“I won't argue about that,” said Strange. He gazed up into the sky, but there was no trace of the dancing fireflies.

Jordan turned, beckoned to Major Blunk. “Get over there to the river,” he ordered. “If there's anything of importance found on that body, let me know at once. Also, see if they can find out what it was that dropped into the river just after he hit.”

“Yes, sir,” said Blunk, and trotted away. Strange searched Jordan's face as the colonel turned back.

“Where else has this happened?”

“At the 81st Pursuit, also the 193rd Bombardment,” Jordan said dully. “Three Handley Pages crashed just before dawn, as they were starting on an early raid. And an entire flight of the 81st was wiped out an hour later. The same story— I didn't believe it at first—those queer red flashes, ships brought down in flames or with the pilots dead—and not another thing in sight!”

“No one has any explanation?”

“Blunk just told me that Chaumont has some crazy idea they're small magnet-controlled bombs dropped from a Zeppelin or a huge plane too high for us to see. They think the bombs explode at a low altitude and are attracted to ships because of the iron in the motors. But I think the idea is preposterous.”

PHILIP STRANGE shook his head. “Too difficult to work out, Colonel—even if it explained the German who fell into the river after the second D.H. crashed.”

Jordan looked puzzled. “But that's the only thing in favor of the idea. He must have fallen from pretty high. We didn't see any ship.”

The G-2 ace stared at him.

“Then you didn't catch it?”

“What do you mean?” exclaimed the colonel.

“That Boche actually came from the center of the ball of fire—or else from nowhere, you might say. One second there wasn't a sign of him—the next second there he was!”

“But that's impossible,” Jordan said hoarsely. “He couldn't have come out of that fire—he'd have been burned to death before he hit the water.”

“Just the same, that's what happened. One of those 'fireflies' suddenly expanded into that mass of flame, and our German dropped out of it. And don't ask me how, because I agree with you—it couldn't happen.”

Jordan's harassed glance shifted across the field, to the crumpled D.H., from which the crash squad was removing two limp forms.

“Poor devils,” he said half under his breath. “I sent them out—the crews of both those ships. I hoped they'd discover some unusual activity on the other side—something to help explain this ghastly business. And now they're dead. Killed by the very thing they were trying to uncover.”

“It's war, Colonel,” Strange said gently. “You're not to blame—it's the fiends back of this thing.”

Jordan's face darkened.

“You're right. And by the Eternal I'm going to find out who they are and even the score!”

“Well, I've a couple of vague ideas I'd like to discuss,” said Strange. “Could we go inside?”

Jordan nodded. “I'd already set aside a room in squadron headquarters—we can talk there without being disturbed.”

Jordan, with Strange following, walked away from the deadline silently and made his way toward the building in the background of the field.

THEY had almost reached the temporary building which served as squadron and also special Corps offices, when a motorcycle sidecar came sputtering up to the door. Blunk sprang out, importantly holding up a charred and dripping map.

“We found this on the body, sir! True, it's scorched and pretty well soaked. But with care I think we'll be able to dry it so we can read it.”

“Anything else on the German?” demanded Jordan.

“Nothing important, sir. Impossible to identify—even if anyone here had by chance known him.”

“What about the ball of fire or whatever it was? Did you find any trace of it?”

“They're trying to find out now, sir. I hurried back with this in case it was important. They're going to drag the river. But it will take at least three hours to get equipment that will do the work.”

Meanwhile, Strange was not forgetting his role of Archie Bye. He now put in a timid question:

“Begging the Major's pardon—but was there any special insignia on the German's uniform?”

Blunk gave him an impatient look.

“With all that mud on it, I didn't see. It's hardly important, anyhow.”

“I—I just thought,” said Strange, “that if he were an air force officer it would narrow down the identity problem.”

“I already told you the man couldn't be identified!” roared Blunk. “And who are you, anyhow?”

“Second Lieutenant Archie Bye, sir, reporting to Colonel Jordan with dispatches from G.H.Q.,” Strange answered, with an arm-jolting salute.

“Humph!” grunted the pot-bellied major. “Well, we can take care of G-2 here without any suggestions from—”

“Good Lord!” Jordan broke in dazedly. “Look out there on the field—the Spad!”

Strange whirled. He had a brief glimpse of a queer mirage-like effect which surrounded the fighter. Then in a flash the Spad was gone!

CHAPTER II. DEAD MAN'S MASQUERADE.

FOR a moment, all three men stood gaping at the spot where the Spad had been. “The ship—it's vanished!” moaned Blunk.

“Any fool can see that!” rasped Jordan.

“Come on,” Strange said swiftly. He started to run toward the point where he had left the fighter, then halted in complete stupefaction. For a fraction of a second, a man's head and shoulders had appeared, seemingly suspended a few feet above the ground where the missing Spad should have been. But these, too, vanished as quickly as they had come.

A whirl of dust and another mirage-like blur followed—then the Spad reappeared exactly where it had been!

Blunk tottered back, his eyes bulging from his head, and even Jordan's pugnacious features had a sickly pallor as Strange turned to stare at him.

“You—you saw it too—the head?” the G-2 chief whispered.

Strange nodded silently, trying to master the primitive fear of the unknown which had come over him. Then cautiously, with Jordan close at his elbow, he started toward the ship. The crash-truck rumbled past, followed by the ambulance with the two airmen's bodies. Strange motioned to an orderly who had been apparently watching the dead men taken from the wreck.

“Corporal, did you see anything peculiar here just a moment ago?”

The non-com looked at him blankly.

“Peculiar? Why, no, sir—I don't get what you mean.”

Three mechanics straggling back from the wreck halted, overhearing the orderly's words.

“Never mind, men,” Blunk said curtly. “We wish to question Corporal Pritchard alone.”

Reluctantly, the ackemmas went on. Jordan confronted the corporal.

“You're sure you didn't notice a sort of mirage—or a man's head—here by the Spad?”

“Let me answer for him, meine Herren,” said a flat, guttural voice from directly behind the three officers. Strange jerked around with the others— then stood paralyzed.

A German Rittmeister in full uniform stood there, a Luger in his raised hand.

“The map, Herr Major, if you please,” he said in the same odd, flat voice. The ghost of a smile crossed his saturnine face as he viewed the stupefied men. “I hope my sudden appearance has not frightened you—but I must have that map.”

Blunk, knees knocking together, held out the chart with a trembling hand. The German reached out for it, his deep-set eyes warily shifting from face to face. The soggy paper was just in his grasp when a shout went up from the three mechanics who had passed by. The German jumped back, tearing part of the map from Blunk's hand. The three ackemmas were dashing back toward the Boche, yelling as they ran.

Flame spurted from the Luger, and the foremost chap to the dispensary.”

In a moment, only Strange and the G-2 chief remained with the Rittmeister. The prisoner stared down at the blood that dripped from his right forefinger, where the trigger guard of the Luger had scraped it as it was shot from his hand. Then he looked up bitterly at Strange.

“Never again will I trust my judgment of a face. Your features belie you, Herr Leutnant.”

“I am not interested in compliments,” Strange said coldly. “Especially from Rittmeister von Kull.”

The German started violently.

“Du Lieber Gott! Who are you? I have never seen you before.”

Colonel Jordan stared at the prisoner.

“You mean this is Paul von Kull, leader of the 55th Jagdstaffel ?” he demanded of Strange.

“Precisely. But we'd better get him inside where we can question him privately before a crowd gathers.”

THE SUN had been down for several minutes and the lights were on when they reached the administration building. Ignoring the questions of startled officers, Jordan led the way to a room at one end of a narrow hall.

“And now, Herr Rittmeister,” he said as he closed the door, “you can save yourself a lot of trouble by talking—and talking fast.”

Von Kull eyed him with a dour amusement.

“You would perhaps like to know how your pilots were killed—and how I came to be on your field?”

“Don't try to be funny!” grated Jordan. “I'll find a way to learn that, my smart Boche!”

“Like most colonels,” von Kull said acidly, “you are filled with your own importance. I may as well warn you that you are wasting your time.”

The cords swelled in Jordan's throat, and a look came into his bulldog face which Strange had never seen before.

“Listen to me, von Kull!” he rasped. “I've never authorized the torture of a prisoner to make him talk. But what happened out there today isn't war! Either we get the answer to that diabolical business—or I'll turn you over to the mates of that man you shot.”

“The killing of a prisoner-of-war will be hard to explain,” retorted von Kull evenly. But some of the color had gone out of his face.

“The shooting of a prisoner who 'tries to

mechanic fell. As the pistol swerved, Strange whipped his hand down to the .45 at his hip. The German whirled, but the .45 roared before he could fire. The Luger went spinning to the ground, shot cleanly from the Rittmeister's fingers.

“Grab him!” shouted Blunk, and the two mechanics threw themselves onto the Boche. With a furious lunge, he hurled one of them aside and raised the bit of soggy paper to his mouth. Before anyone could stop him, he had gulped it down. Purple with rage, Blunk snatched up the Luger, aimed it pointblank at the German. But Strange knocked it out of his hand.

In the next instant, stark amazement drove thoughts of the doomed D.H. from Philip Strange's mind. For those tiny red blurs had abruptly spread into a large, dazzling ball of flame— and from out of that ball pitched the figure of a man!

“You young whelp—I'll have you court- martialed for that!” howled the fat staff officer.

By an effort, Strange held his temper and remembered the timid role he had been ordered to play.

“S-sorry, Major,” he stammered. “But if you had killed him we couldn't get any information from him.”

“Lieutenant Bye is right,” Jordan said gruffly. “Major Blunk, I'll take the rest of that map. And suppose you and the Corporal see to getting that wounded man into the first-aid shack. We'll take care of the prisoner.”

Crestfallen, Blunk obeyed. At a surreptitious nod from Strange, Colonel Jordan turned to the two mechanics, who had angrily seized the German.

“We can handle him, men. Help them carry that escape' will be quite simple to explain,” Jordan said grimly. “Especially when the Chief of Intelligence is the one who makes that report.”

Von Kull's gloomy face froze with sudden defiance.

“Very well, Herr Oberst, bring on your verdammt assassins.”

“I will!” fumed Jordan. He whirled toward the door, but Strange caught his arm

“Wait, Colonel, there may be a better way. Even if he talks, he will only lie to you.”

“Well, then what else can we do?” growled Jordan.

“We might look at that map. It's barely possible that von Kull's appetite wasn't sufficiently large.”

Jordan spread the map on a desk, while Strange watched the prisoner.

“It's a Boche sector-map, covering the Luneville-Rondecourt area on this side and part of their trenches across from here,” the G-2 chief reported. “Here's a pencil line drawn from Rondecourt to somewhere in Germany. But that's the part this blasted Hun swallowed.”

“We could use a stomach-pump,” said Strange. “But the line probably wouldn't be legible. Can you see any other marks?”

“No, but the 55th Staffel isn't in the section torn from the map, if that's what you're thinking. They're farther north.”

“Can you get an accurate bearing on Rondecourt from that pencil line?” asked Strange.

“It's on a bearing of 157 degrees from Rondecourt to the place where the map's torn,” Jordan announced after a minute. “Why?”

“Because I'm going to fly back along that course,” replied Strange. “Now, Herr Rittmeister, if you'll kindly remove that uniform—”

“I refuse!” snarled von Kull.

“A little tap on the head with this .45 ought to take care of that,” Strange said calmly. “I'll give you five seconds to make up your mind.”

Von Kull glared at him, but under the cold regard of the G-2 ace he lost some of his belligerent manner. Sullenly, he began to take off his tunic.

“Zum Teufel!” he muttered. “I cannot understand it—you talk like a lion, and—”

“—and look like a mouse,” Strange finished dryly. He glanced sidewise at Jordan. “Colonel, if you'll cover our guest for a few minutes, the mouse will make a slight transformation.”

Jordan took the gun, and Strange quickly removed his boots and his uniform. As he donned the prisoner's clothes, von Kull laughed scornfully.

“Simpleton! You will give yourself away ten seconds after you land in Germany.”

“I think not,” said Strange. He took the makeup kit from his flying-coat, gestured for the half-clad German to sit down across the desk, then seated himself before the propped-up kit. Jordan watched nervously.

“Think what this means,” he said in an undertone. “He'll know the truth about you.”

“I know,” said Strange. “And I'm afraid we'll have to hold him incommunicado for the rest of the war—but a little solitary confinement may do him some good.”

VON KULL watched with puzzled, hostile eyes as Strange prepared to remove the makeup. Moistening a small sponge with a special solution, the G-2 ace rubbed it across his face. The greaseless paint disappeared, and with swift- moving fingers he plucked the tufts of scanty yellow hair from his upper lip. Straightening up from behind the kit, he smiled ironically at von Kull. The German leaped to his feet, eyes dilated as though he saw a ghost.

“Gott in Himmel!” he whispered. “The Brain- Devil!”

Strange inclined his head mockingly. “The mouse has staged a vanishing act. You see, mein Freund, you are not the only magician—even though I cannot make a Spad disappear.”

“The fools!” raged von Kull. “They told us you were dead and buried!”

“And so,” said Strange, “this becomes a dead man's masquerade.” He set out a row of paints and lining pencils, and in a few seconds the fierce, gloomy features of Rittmeister von Kull began to take shape against the background of his own face. His whimsical expression quickly faded, became hard and forbidding as his nose lengthened and his lips assumed a thin, pinched look. Bits of black crepe hair, affixed at the bridge of his nose with spirit gum, joined his scowling brows just as von Kull's met across his nose.

“You still will not fool them!” snarled the prisoner.

Strange's head jerked up from the mirror.

“Silence, swine!” he rasped, in such a perfect imitation of von Kull's expression and voice that the German's jaw dropped. With a soft laugh, Strange got to his feet. He closed the makeup kit, buttoned the tunic, and took the .45 from Colonel Jordan.

“We'll have to wait a little while, until most of the men are at mess. I don't want to stage this 'escape' with guns blazing around my head.”

“What's your plan?” Jordan said brusquely.

“I'll use the Spad. You might phone word in a few minutes for one of the men to fuel it up and start the motor. By that time, mess call will have sounded—even an ugly affair like this won't keep men from eating. Then when the way is clear, I'll go out the side door and take off as quickly as possible. As soon as I'm in the air, give the alarm that the prisoner has escaped. You'll have to keep von Kull in here, out of sight, until you can sneak him away in a car late tonight. It means taking Major Blunk partly into the scheme—but you can simply tell him that 'Lieutenant Bye' is working with you on a special plan. He won't have to know who 'Bye' really is.”

“But why the need for giving the alarm about your escape?” interposed Jordan.

“To fool any Boche spies who might be on this field. And I've a hunch there are some, from the way von Kull got here so easily.”

“Dumkopf—you are a million miles from the truth!” von Kull flared up. “Right under your nose is—” he clamped his teeth together, gave the two men a sneering smile. “But go ahead, Herr Strange—don't let me interfere with your pretty little scheme.”

“I'll try not to,” replied Strange. He glanced at Jordan. “It might be a good idea to have a 'Plan Two' order flashed to three or four squadrons.”

Von Kull shot a shrewd look from Strange to Jordan.

“Ach! A concentration of air force, nein? Don't bother yourself, Herr Oberst, this 'dead man' of yours will bring back no information to warrant a raid. This time he will stay dead!”

TWENTY MINUTES LATER, von Kull's words came back to Strange as he stole across the deserted field to the idling Spad. There had been a gloating note in the German's voice, as though he visualized something beyond their knowledge. But Strange put that grim prediction out of his mind and climbed into the waiting ship, after pulling the chocks aside. Then sliding the makeup kit into special clips under the seat, he fastened his belt and opened the throttle.

The afterglow was fading, but the field was still far from dark. He taxied out only a few yards, quickly swung into the wind, then opened the ship wide. The Spad darted forward, gave a sharp lurch, then straightened under hard rudder. Strange stared back, but there was no obstacle to be seen, nothing to explain that sudden jerk to the side.

He climbed steeply, following a course of 167. A minute passed, and back on the field A-A guns abruptly cut loose with a vain barrage. Colonel Jordan had timed the alarm perfectly. With the Hispano almost full out, Strange held an altitude of five thousand feet until he was nearing the Front. Here he began to climb again, gliding down into the dusk as soon as he was out of range of the frontline batteries.

In a few minutes more he was flying over hilly and wooded terrain where, because of the nature of the ground, the Germans had never established any flying-fields. He sat back, mechanically keeping his eyes open for dusk patrols, meantime going over in his mind the salient points of the mystery.

It was obvious now that the crews of the two D.H.'s had not seen whatever it was that had sent them down, at least no more than he had. The observers had simply been firing at random, hoping to hit the source of the invisible doom that struck at them. And those holes in the Spad's tail and wings—they had certainly looked like bullet-holes. If bullets had made those holes, then they could only have come from the dancing red fireflies—and that seemed impossible, until the sudden expansion of the tiny red blur into that vast ball of flame from which the German had fallen.

There was only one answer, if he were still to credit his senses with having seen that bizarre occurrence. By some scientific trick, the Germans had managed to achieve—

T-t-t-t-t-t-t-t-t! Strange jumped, hurled the Spad into an Immelmann. For the second time that day bullets from nowhere were hammering into his wings!

CHAPTER III. DEVIL'S DROME

ON TWO SIDES, the now familiar red fireflies whisked up after him. In the dusk, they were brighter than before, and their weird, flickering dance was like the flash of fire from machine-gun muzzles—like Spandaus winking in the gloom . . . .

Strange's pulses leaped. That was the answer! Those darting fireflies were the muzzles of chattering guns, somehow rendered invisible except for their tips.

“And Spandaus don't fly by themselves!” he flung savagely into the slipstream. Where there were machine-guns in the air, there had to be ships. And even an invisible plane could be hit by Vickers slugs!

Forgetting his first plan for the moment, he whipped around and tripped a burst back of the nearest flickering blur. The blur vanished, but another one swiftly came into sight above and to the left. Strange gave a shout of triumph.

He was right! That unseen devil had pulled into a steep chandelle and was diving back at the Spad. With a tight vertical turn, he rolled inside of the tracer-less burst which was gouging at his tail. The red blur shot past, disappeared. In a twinkling, Strange kicked back to align his guns on the invisible ship. If he had gauged it right, this time he could not miss.

The Vickers throbbed eagerly at his touch. A long burst smoked from the guns before he remembered the scheme he had outlined to Jordan— his impersonation of von Kull. He jerked his hand from the trips, zoomed with the Hisso wide-open. Even now it might not be too late. He would still have an excuse if they demanded one. . . .

Two crimson blurs now appeared below him, moving swiftly upward. Either he had missed—or it was another of the invisible ships. He snatched at a flare-release, rolled to one side as the light blazed up. In the brilliant glare, the muzzle flames of the unseen guns were lost. He cast a tense look back of him, then plunged beneath the flare. It was a desperate chance, and if the plan failed he was doomed. But one of those invisible devils would probably get him, anyway, if he tried to escape.

Two hundred feet beneath the flare, he brought the stick back and banked into a circle. Leaning out, half-blinded, he pointed frantically to his face. A drumming of bullets into the Spad's right wing answered him—then the pounding abruptly ceased. Hardly daring to hope, he spiraled down in the glow, still gesturing to his made-up features. He had an uncomfortable feeling of sharp eyes staring at him, and once he felt the ship sway as though it were in the slipstream of some unseen plane passing close by.

The Spad was down to three thousand feet when a motion of something at the same level caught his eye. He turned his head, and barely repressed a violent start. Less than a hundred yards away, a man's head and shoulders had appeared—exactly as he had seen them for an instant back at the 366th. They seemed to be floating downward at the same angle as the Spad, and as he ruddered closer he saw the man raise his right hand in some sort of signal.

It was then that he saw the rim of a cockpit encircling the half-visible figure. Over the man's shoulders he glimpsed a large glass screen above the center of an ordinary-looking instrument board such as might be found in a Fokker D-7. He could even see the top of the control stick in the hands of that mysterious figure, but of the plane itself there was not the slightest trace.

Apparently some kind of hood which had made the entire cockpit invisible had been slid back. Strange noticed a queer shininess at the top of the cockpit rim, like mirrored glass, and directly under it was a misty blur that added even more to the fantastic appearance of the floating cockpit. But he had no time to scrutinize the pit more closely, for the Feldgrau-clad pilot was pointing down and watching him inquiringly.

Strange nodded, hoping that his disguised features hid the tension he felt. If the German suspected him for an instant he would simply close off his cockpit again and vanish for another attack.

The mysterious cockpit tilted slightly, angling away from under the flare. Strange followed, keeping parallel, but ready for a hasty swerve back of the invisible ship if the occasion should demand it. The Boche bent over his controls, touched something on the instrument board, and two streams of luminous smoke poured from where Strange judged the invisible wingtips to be. Evidently the pilot intended these as a guide, for he at once swung in ahead of the Spad, gliding at a sharp angle.

One burst, and Strange could have riddled the man in the cockpit. But it would not have solved the problem. He followed carefully, a hundred feet behind the invisible ship, until the flattened angle of the cockpit showed that the pilot was leveling out.

In dismay he saw that there were only trees below and ahead. The ships were down in a valley, with trees on both sides and a dark cul-de-sac beyond. He was about to open the throttle and zoom to a safer height when to his astonishment the Spad's wheels touched a flat, solid surface and he found himself rolling along above the tops of the trees.

“Glass!” he exclaimed. “It's a glass runway!”

HE HURRIEDLY CLOSED the throttle, for the cockpit of the invisible ship was slipping back toward him. Then, at taxi speed, he slowly followed the other man, keeping in between the two streams of luminous smoke. It was possible that the smoke streams were intended for the purpose of lighting the runway, though he still could not see the shiny surface he had expected. Either that, or they were used at night to warn the pilots of other invisible ships if they came too close in the air.

He had taxied about two hundred yards when the man in the floating cockpit lifted his hand in a signal to stop. Strange throttled his motor, with the grim realization that the die was cast. Even if he wished, he could not turn and escape now. With an odd fascination, he watched the German stand up in the cockpit, his legs suddenly appearing as if from nowhere. The pilot jumped down, motioned to someone in the darkness ahead.

Two gigantic tarpaulins on which trees had been painted slid apart at his signal, and Strange could dimly see an enormous platform which had evidently been erected on piles. Faint blue lights bobbed through the gloom, and a dozen men hurried forward. Six of them went to the rear of the invisible ship, feeling their way to wingtips and tail. As they pushed it ahead, the other men ran back to the Spad and shoved it into the secret base. With a silent prayer that it was not forever, Strange switched off the Hispano.

The tarpaulins closed behind him, and the blue lights brightened, revealing methodically arranged cubicles along one side and also at the rear of the platform, apparently quarters for officers and men. The rest of the base appeared to be unoccupied, but with a sudden thrill that was half consternation, Strange caught sight of a huge motor and part of a wing section seemingly suspended in midair. Then he knew that a giant ship, invisible like the fighter, filled that space, one engine-cover evidently lifted for repair work—the only proof that the space was not empty.

Leaning against the wall were several sections of peculiar-looking glass, two of them curved like the fuselage of a Fokker. But instead of showing the wall directly beyond, a cubicle doorway was eerily reflected, although the cubicle itself was at least sixty feet distant. Strange took a second quick glance, and the secret of the invisible ships began to dawn upon him.

The Germans had evidently developed some new type of glass, with the property of bending light rays at sharp angles or curving them so that lines of vision would be sharply deflected instead of going through to what lay beyond. In addition, the glass seemed to be opaque on the inside surface, so that no light would show through and whatever it covered would be hidden, and from its use as a runway Strange knew it must also possess prodigious strength.

With molded glass propellers, and panels covering wings, fuselage, control rods, the motor and seemingly even the guns, the ships could only be seen by someone wearing glasses of the opposite refraction. Otherwise, all lines of vision from outside would be led off or curved so that, in midair, only the empty sky would be seen, except by some rare accident when another ship in a battle might be aligned with the bent rays. In such a case, the other plane would appear to shift position suddenly, or if blanketed at a certain angle, would seem to vanish.

This was precisely what had happened to the Spad, back at Rondecourt, and with that realization Strange knew how von Kull had been able to land unseen. The Rittmeister had simply been flying one of the invisible ships, and, seeing one of his pilots shot down, had landed to be sure no clue was found. His glass-enclosed ship had momentarily stopped before the Spad, as he prepared to climb out. Seeing he was observed as he slid back the glass cockpit-enclosure, he had closed it and taxied away from the Spad, then emerged again when no one was watching. It was undoubtedly the wingtip of the invisible ship which the Spad had grazed in taking off. In short, von Kull's ship was still on the field at Rondecourt!

A dozen other details surged into Strange's mind, half-cleared by the discovery of the mysterious glass. But he had no time to consider them, for the pilot who had guided him down was hurrying back to the Spad, followed by another German in the uniform of an Ober-Leutnant of the Imperial Air Force. The first Boche was small and dapper, but the senior lieutenant was a hulking German, with a round, red face that just now held an angry look.

“Herr Rittmeister!” exclaimed the dapper pilot, as Strange climbed from the Spad. “What happened? We thought you were a prisoner.”

“I was, but I tricked the verdammt Yankees!” grated Strange.

“Is that any reason for trying to shoot me down?” broke in the Ober-Leutnant fiercely.

“Leutnant Janner, don't forget this is der Rittmeister! “ exclaimed the other pilot.

“I'm aware of that,” Janner said harshly. “But I'm not offering my body on the altar, Rittmeister or no Rittmeister.”

STRANGE saw the faces of the assembled men, and he knew it was time to take care of Janner before he got completely out of hand. He took a quick step and drawing back his glove slapped it smartly across the German's face.

“Next time, schwein, think twice before you address your commanding officer in that tone!”

A tense silence fell, and for a moment all eyes were on Janner and the white mark the glove had left on his face. Strange stood glaring into the other man's eyes.

“If you had stayed to see what happened, you would have seen me escape, and there would have been no mistake. It was your own fault!”

“If you had signaled, I would not have attacked,” mumbled Janner.

“And what was I to signal with?” Strange said sarcastically. “I was lucky to escape with my life, without stopping to ask for a rocket-pistol.”

The other man lapsed into a glowering silence. Strange turned to the staring mechanics.

“Get back to your posts,” he snarled. He waited until they had scurried away, then turned back to Janner. “The score is even—you fired on me, too. But neither of us is hurt, so the matter can be forgotten. Besides, there is more important work at hand.”

“What about your plane, Herr Rittmeister?” said the dapper Boche anxiously. “Has it fallen into the enemy's hands?”

Strange seized on the opportunity thus provided.

“Not yet, but they may discover it at any moment. I was unable to reach it when I broke away, and this Spad was the only ship that was started. The plane must be destroyed at once before they can learn the secret.”

“Let me go,” said the little German eagerly. “I would like another chance at those Nuenglander pigs.”

Strange shook his head.

“This mission calls for a larger ship.”

“Mein Gott!” Janner broke in. “You would risk the Gotha on such an errand?”

“Let me finish!” snapped Strange. “It so happens they are concentrating five squadrons at the old bombing-depot field west of Rondecourt. If we move fast, we can destroy them within an hour.”

Janner's expression became a trifle less sullen.

“Five squadrons! Ach, it should get each of us the Pour le Merite —and furloughs in Berlin!”

“There is no time to waste,” Strange said tartly. “How soon can the Gotha be ready?”

“As soon as the bombs are loaded, and that panel closed on the starboard motor,” replied the big Ober-Leutnant.

“Start the crew to work, at once,” Strange ordered. “I'll give you the detailed instructions afterward.”

“Very well,” grunted Janner. “I will see you in the operations office.”

Strange turned to the other Boche as Janner stalked away.

“Has anything important happened while I was gone?”

“Ja, Herr Rittmeister—a message of approval from the High Command. Full details of the first two attacks were sent to them by separate observers, and the Field Marshal is greatly pleased with these first tests. He has ordered a full flight of pilots here, as you requested, from your old 'Staffel'. They will arrive before morning. And the High Command also agrees to your keeping all commercial rights to the Kullglass, if you will turn over the formula to Army chemists for mass production.”

Strange hid his surprise at the last statement. He had not known that von Kull was other than the usual Prussian officer. If he were the inventor of the invisible glass-shielding, then Jordan had a more important captive than he had thought.

“We had better go back to the office,” he said shortly.

“But, Herr Rittmeister, if I am to have my plane refueled and ready—” The dapper pilot looked at him with puzzled eyes.

“Jawohl, go ahead,” muttered Strange. “But meet me at the office as soon as possible.”

The German hastened toward his ship, of which only the opened cockpit still was visible. Strange looked around quickly, started along the row of cubicles. The office would probably be the largest. And if he knew anything about von Kull, that office would contain some highly important maps, perhaps even some operations orders of vital interest to Chaumont. If he could include these also in his wild scheme . . .

“Was ist, where are you going?” a harsh voice spoke up from his left. He wheeled, saw Janner in front of a door with a blue light over it.

“I was thinking of something else,” Strange answered curtly. He opened the door, jerking his head for the big German to follow. “I didn't realize I'd gone past the—”

HE stopped short, for the room was furnished as sleeping quarters instead of the office he had expected. Janner had come in behind him and was staring at him intently. Aware that the bright light was shining straight on his face, Strange took a step to one side.

“Wait!” Janner said tensely. “Why were you going that way—when the office is back by the entrance?”

“Where I go is my business!” rasped Strange.

“Not if you are trying to cheat me out of my share in the Kullglass formula,” Janner said fiercely. “I half believe you were trying to get rid of me tonight.”

“Don't be a fool,” Strange retorted. “How could I tell whose plane it was?”

“It was an even chance that it was mine,” Janner flung back harshly. His eyes had a furious look. “If I were sure—”

“Get out of my way,” snapped Strange.

The blood rushed into Janner's face, and with an oath he lunged at the G-2 ace. Strange jerked back, and Janner's fist struck only a glancing blow across his face. The infuriated German rushed in again, like an angry bear. Strange sidestepped, drove a left hook to the Ober-Leutnant's jaw. It rocked Janner's head, but failed to stop him. Strange snatched at his .45, to cover the Boche before the struggle brought others to the scene. But with another bear-like lunge, Janner struck against his gun-hand and he dropped the weapon. Before he could reach it, the Ober-Leutnant whipped out his Luger.

“So! You would kill me!” he panted. Then a look of astonishment came into his eyes. He stared at the bridge of Strange's nose, then down at his own knuckles, and with dismay Strange saw bits of crepe hair sticking to the German's hand.

“Lieber Himmel!” Janner said in a stunned voice. “You are not von Kull!”

Strange waited, motionless, aware that the slightest move would bring a shot from Janner's gun. The German's eyes bored into his made-up features as though he would pierce the disguise and see what lay beneath.

“Who are you?” he said tensely. “What have you done with von Kull?”

Strange made no answer. Janner backed toward a table beside his cot, picked up a telephone with his left hand.

“Send Leutnant Braun here—and the guardsergeant—quick! Something has happened to von Kull!”

Strange groaned and closed his eyes for an instant, as though he had given up hope. Then in a desperate flying-tackle he dived headlong at Janner's knees.

CHAPTER IV. INVISIBLE DOOM

THE LUGER BLAZED just above his head, and the report echoed thunderously in the cubicle. Knocked off balance, Janner went crashing to the floor. Strange landed a fierce blow under his ear, and the Ober-Leutnant collapsed limply. Excited voices sounded from out in the base. Strange hastily pulled part of the tufted crepe hair from the back of Janner's hand, pressed it to the vacant spot between his eyebrows. He had barely finished when two round-hatted German mechanics burst into the room. They halted, staring slack-mouthed at the inert figure on the floor.

Strange coolly picked up the .45 and the Luger and rose to his feet. The dapper Leutnant came running into the cubicle, followed by an armed guard-sergeant and half a dozen Heinies. Strange gestured to the unconscious Janner.

“Sergeant, tie up the Herr Offizier before he recovers his senses and tries another murderous attack.”

The non-com knelt beside Janner. Strange turned to the undersized lieutenant and held out the Luger.

“Smell the muzzle, Leutnant Braun. You will note that the gun has just been fired. The empty shell is there on the floor.”

“Ja, Herr Rittmeister,” said Braun breathlessly. “It is so. But I—”

“The gun is Leutnant Janner's,” Strange went on tersely. “You will find the bullet-hole there in the door, proof that he fired at me. I am telling you this so you will be ready to testify at the court-martial, later.”

“But why did he try to kill you, Herr Rittmeister?” exclaimed Braun. “They told me that he phoned that something had happened to you.”

“I think he intended to make it seem an accident—but I was too quick for him. He called me in here and caught me off guard. But while he was telephoning, I managed to retrieve this pistol which I stole back at Rondecourt. Janner made the error of putting it a trifle too close to me after he disarmed me. I hurled it into his face just as he fired at me.”

“I knew he hated you,” said Braun, then reddened in confusion. “Your pardon, Herr—”

“It is of no importance,” Strange interrupted. “But now we have other things to do. Is the Gotha ready?”

“It will be in another minute. Unter-Leutnant Schwartz is ready to start the motors when you give the word.”

“Tell him to start them at once,” Strange ordered. “I will take the plane Janner flew, if it is in condition.”

“Ja, your bullets—the ones you fired by accident,” Braun hastily amended his sentence, “only chipped the Kullglass on the cowl. I have had the tanks filled and the guns reloaded.”

“Sehr gut,” Strange said crisply. “Have the plane ready to take off after the Gotha, and you will follow me. Tell Schwartz to circle at two thousand feet until we are at his altitude. We will approach Rondecourt at ten thousand and begin gliding to bring us in at a thousand feet. You and I will take care of any Allied planes in the air, while Schwartz goes low enough to destroy the fighter I had to leave on the field. After that, we will raid the concentration field to the west. Is that clear?”

“Yes, Herr Rittmeister—it is an excellent plan.” said Braun, with a fawning smile. “I will tell Schwartz at once.”

He hastened out. Strange turned to the guard- sergeant, who had tied Janner to the bed with a rope brought by one of the men.

“That will be all. The prisoner will not need a guard—at least until after we have taken off. Go out and help clear the way for the Gotha—that Spad will have to be moved.”

The sergeant and the other Heinies shuffled out. Strange gave a long sigh of relief, for Janner's eyes were starting to twitch. He tore off part of the German's shirt and gagged him securely. Janner was glaring up at him as he finished.

“Auf Wiedersehen,” Strange said ironically, “unless your superiors decide to shoot you for bungling.”

He took both the .45 and the Luger, went out the door, and glanced swiftly around the base. From the position of a gangway-ladder near the entrance, he could tell where the invisible Gotha stood. Its unseen motors were rumbling, but after a moment the sound died to a faint drone as silencers were cut in. Over to one side, the opened cockpit of an invisible fighter seemed to float in the air, as before. The blue lights had been dimmed again, but after a few seconds he was able to locate Braun's ship, which like Janner's had its Kullglass hood slid back, exposing the empty cockpit.

The Spad's motor had been started, and an Unteroffizier stood beside it, fastening on helmet and goggles. Strange looked around, then he saw the reason for the motor's having been started. The Spad had been placed so that the Gotha could take off, but in the limited space remaining the two invisible fighters would have to be jockeyed carefully to get around it. Braun or one of the others had evidently decided to have the Spad flown to some regular field, to clear the way for the two fighters when the Gotha had taken off.

THE HUGE TARPAULINS were already opening. Strange hurried across to the cockpit of the first Kullglass ship, his nerves suddenly taut. If he slipped up now, his plan to get rid of the invisible ships would boomerang with frightful results. Disaster would again strike Rondecourt, and even though he had given a false location for the squadron concentration, those devils in the Gotha would certainly unload the bombs within that glass hull before they returned.

He could feel the slipstream from the Gotha's motors and from the Spad, but the engine of Janner's fighter had not been started. He felt his way along the trailing edge of the wing, stooping to look closely at the Kullglass surface. Even a foot from the wing, he failed to detect the glass itself. But its bent rays picked up the side of the wall, creating an eerie effect.

The Gotha's invisible motors now speeded up, sending a gale whistling back into the base. Strange clutched the rim of the cockpit, hastily scrutinized its interior. Except for the glass screen mounted above the instrument board, it looked like the usual cockpit. But when he peered through the frosted glass he saw the final explanation of the ease with which von Kull's pilots had handled their unseen ships.

The screen, obviously made with the opposite refraction from the rest of the fighter's glass panels, neutralized the bending effect, so that it was like looking through a windowpane, though the screen was ten times thicker.

Strange climbed into the cockpit, made a quick examination of the guns. They seemed to be Spandaus, but he could not be sure, for a heavy sleeve of the Kullglass covered all but the breeches, which extended back into the hooded space. He watched through the glass screen, and was electrified to see the ponderous shape of the Gotha appear as it taxied out onto the ramp. Through the frosted glass, it looked like an ordinary bomber completely covered with ice even to the strut wires, which ran through narrow glass sleeves. But when he looked outside the cockpit, the Gotha vanished.

He watched it begin its take-off, then stood up in the pit and shouted for a mechanic. Leutnant Braun came running, with two helpers at his heels.

“The Gotha will be off in a minute, Herr Rittmeister. Our motors are still warm, so they will start at once.”

“Start them now!” Strange barked. He set the switch as one of the men signaled, and the motor under the glass-shielded hood came to life with a hissing sound.

Braun had darted back to the other fighter, and the man in the idling Spad was about to taxi onto the ramp, when a bell jangled loudly from up at the entrance.

Strange thrust his head out the side of the cockpit. The men at the entrance were scattering hurriedly, and in a second he was startled to see two plumes of luminous smoke appear. He took a swift look through the glass screen, and went rigid as the outlines of another invisible fighter suddenly were revealed.

The ship whirled in a tight ground-loop, just missing the Spad and stopping in the space where the Gotha had been. Then the cockpit hood slammed back, and a disheveled figure leaped out.

It was von Kull!

A chorus of shouts went up, and Strange saw the guard-sergeant push through the crowd of mechanics. He jerked his own cockpit hood almost shut, leaving only a crack through which to see. Von Kull's furious voice abruptly silenced the rest of the Germans.

“Stille, you blockheads! Get Leutnant Janner here!”

“But, Mein Herr,” faltered the guard-sergeant, “you had him tied up—you were here—”

“Grosser Gott!” roared von Kull. “Do you mean that swine of a Yankee has been here?”

Strange saw Braun sprint past, his face pale with consternation.

“Herr Rittmeister!” he moaned. “I don't understand! “You were here—how did you get out there in that ship?”

“You blundering Ochs!” stormed von Kull. “I just escaped from Rondecourt. But for our agent, Pritchard, I'd have been finished.”

“B-but I saw you, Excellenz!” groaned Braun.

“You saw that verdammt American they called the Brain-Devil—Captain Strange! The report of his death was false. He made-up to pass for me after I was captured—and now you fools have let him escape with the secret!”

“But he hasn't escaped!” shrilled Braun. “He is still here—he's in Janner's ship!”

“What?” howled von Kull. “Then what are you waiting for? After him, you Dumkopf!“

Braun whirled, drawing his pistol, then a helpless look came into his face. “He's closed the hood! I can't tell where the ship is!”

Von Kull spun around to the group of mechanics.

“Spread out! Form a line and find that plane— it's got to be over there in the rear space.”

STRANGE had shut the hood completely as Braun drew his gun, but through the frosted screen he saw the mechanics hastily link hands. He cast a desperate look toward the entrance. The Spad and von Kull's fighter blocked his chance of taking off, but if he could reach von Kull's ship . . . .

Jerking the Kullglass hood partly back, he thrust his .45 outside and blasted two shots over the heads of the advancing Germans, and with wild yells they broke and ran. Braun's pistol blazed, and a bullet ricocheted from the cowl shielding. Strange pumped a shot at him, and the Boche slumped to the floor. Von Kull seized the fallen man's gun but before he could fire, Strange pulled the hood shut and cracked the fighter's throttle. The ship lurched forward with a muffled drone of its glassed propeller. He snapped the throttle shut, emptied the .45 into the frosted screen and rammed the hood open.

Von Kull gave a shout as he leaped from the opened cockpit. One shot spurted from his gun, then Strange was hidden as he ran along behind the moving invisible ship, with the bending rays of the Kullglass shielding him.

Strange now took a quick glance at the cockpit, saw that the plane was slowing down. Ducking to avoid bumping the unseen wing, he raced toward von Kull's ship, still marked by its open cockpit.

“There he goes!” bawled a furious voice. Janner, released by the guard-sergeant, was charging toward Strange like an enraged bull, and the G-2 agent's heart surged when he saw he could just reach the cockpit in time to escape. He spun around, with bullets whistling past his head, then vaulted onto the wing of the Spad. A slug crashed the compass-bowl, flooding broken glass and alcohol back onto him. But he made the pit and shoved the throttle open.

Von Kull bellowed for the tarpaulin-curtains to be closed, but the Spad roared through and plunged down the glass runway.

The abrupt change from light to darkness almost blinded Strange. He leaned out, straining his eyes to see. He expected at any second to plunge off into the trees.

The Spad's rudder jumped under a sudden pounding at the tail. One of the invisible fighters was racing down the runway directly behind him!

With a flash of inspiration, he pulled the toggle of his remaining flare. A welcome, brilliant light leaped up behind him, and just in time he ruddered away from the out-flung branch of a tree. The next second the Spad's wheels lifted, and the ship thundered up from the valley.

Strange flung a glance below, saw the flare tossed violently from the runway. Hardly had it struck the trees when, a hundred feet beyond, limbs and branches broke from a sudden impact. Dazzled by the glare, the pilot of the pursuing invisible ship had veered from the runway and crashed.

Fire was spreading through the treetops, where the flare had been hurled. As Strange pulled up in a steep climb he saw the flames blown back sharply for a moment, and he knew that one of the other invisible ships had passed by safely. In a few moments more that ship would be on his tail!

He looked up tensely into the sky, hoping against hope that there would be some unshielded spot on the Gotha. But the empty sky mocked him.

Throttle against the peg, he sent the Spad up in a fast spiral, knowing that somewhere above him invisible doom was circling. If they opened fire without waiting for point-blank range, he might have a beggar's chance. With icy fingers taut on the trips, he kept on climbing.

AND THEN it came! A vicious, battering hail that riddled the upper right wing before he could move the controls. He rolled madly to the left, eyes probing the night. There they were, two flickering red eyes, the muzzles of a twin-mount tilted down from the unseen Gotha!

Bow-guns—or rear tourelle? There was no way to tell. He whirled the Spad in a tight renversement, stabbed a burst back of the deadly red blurs. The flickering spots vanished, but two more appeared just back of where they had been. Strange sent the Spad screaming up into an Immelmann.

Now he knew! Those first blurs had been from the bow-guns. The ship was headed west, and he was almost above it. Another burst spouted from his guns, and with a shout of triumph he saw the tracers end abruptly in space. He had hit the invisible ship. Now if he could only find a vital point . . . .

Something flashed against the light from the burning trees beneath. He whirled, saw two more crimson spots darting in at the Spad. But this time no unseen ship hid the source of those deadly fireflies. The hood was open, and crouched in that weirdly plunging cockpit was Rittmeister Paul von Kull!

It was Janner, then, who had seized von Kull's ship and had crashed from the runway in his headlong pursuit. And von Kull, leaping into the ship Strange had left, had failed until too late to see the bullet-shattered screen. Helpless, he had been forced to open the hood.

Mad with fury, the Rittmeister charged in at the Spad. Strange spun the ship on its wingtips, swiftly nosed down. The Gotha's guns had gone dark, but the crimson blurs frantically burst forth again as he dived. With those flaming muzzles not a hundred feet from his prop, he hauled the stick to his belt.

Too late, von Kull saw those deadly red spots which the diving Spad had kept hidden from him. There was a grinding roar, and the Rittmeister's ship crashed into the unseen Gotha.

Flame gushed from midair, swept back at the horrified German. For one dreadful moment, Strange saw him claw at his belt in a frenzied attempt to jump. Then the rushing flames engulfed him, and the two invisible ships, locked in a fiery embrace, went whirling down the sky.

THE BLAZING WRECKAGE struck in the heart of the valley, and with a terrific explosion the bombs went off. Trees and bits of flaming, shimmering glass spouted up in all directions, and when the air had cleared a wall of fire blocked the entrance to the base. Strange shivered, for he knew no living thing would be left when the fire was through. Von Kull was gone—and with him the secret Philip Strange had so craftily guarded—the secret that he was alive.

Banking toward the Front, Strange took the makeup kit from under his seat. Back at Rondecourt, Colonel Jordan would still be waiting for “Second Lieutenant Archie Bye” to report.

A grim smile touched the lips of the G-2 ace. Von Kull's savage prediction of his doom had almost come true. But not quite. For the “dead man” was coming back—alive.

Table of Contents

By Donald E. Keyhoe

CHAPTER I. THE BOCHE FROM NOWHERE.

CHAPTER II. DEAD MAN'S MASQUERADE.

CHAPTER III. DEVIL'S DROME

CHAPTER IV. INVISIBLE DOOM