I finally returned from the conference in New York, hoping to get back to some real work, only to find myself plagued by constant interruptions. Maybe if I keep my head down and ignore him he'll go away.

He hrrumphs again and I realize it's hopeless.

"Detective Dave Johnson, doc."

I had heard him the first time. I kept trying to concentrate on my work. The problem with the beam energy dissipation with distance was becoming disturbing. "You know, of course, about Doctor Rialson's death."

I decided to just nod. The trouble kept coming down to the increasing static in the low frequency bands as the focus distance increased. I was beginning to worry that I'd have to back up and try a different approach, a possible loss of weeks.

"I hope I'm not disturbing you?"

Lord forbid. "You are."

"But I think you might be able to help me."

"I doubt that."

Damn that conference. I suddenly realized he was bothering me because I'd been out of town and was therefore above suspicion. Back to the matter at hand, maybe if I thought in terms of pulse frequency instead of pulse synchronization.

"Dr. van Keising said you were in charge of the linear accelerator."

"Among other things."

"Yes, well, according to the coroner's autopsy, Dr. Rialson died of radiation poisoning."

Odd, but irrelevant. "What does that have to do with me or the accelerator?"

"The coroner couldn't find any radioactive material in his body or at his apartment. I thought possibly the linear accelerator was used on him."

Nuts. I sighed and looked up. "And how did they get it to his apartment? It's only 100 feet long." Now that I had no choice, I looked the cop over. He appeared to be in his early fifties, bald and slightly overweight. He also looked to be on the verge of a fit of apoplexy, which might be amusing.

"Could it have been used on him here?" He was holding his frustration in quite well. Too bad.

"Sure, if he was tied to the beam exit for 10 minutes while a two man crew operated the thing. By the way, we have a tape record of all uses of the beam. I'm sure it will show that they were all authorized." I looked down at my papers again.

"Will you check . . . please?"

"I'll have a grad student look at the tape when I have the chance. Good day." And good riddance.

Later in the day, mainly for fun, I had one of my students look at the tape. Of course all uses of the Linac were legal. Assassination by particle beam! What next? On the other hand, what about a beam weapon mounted on a high resolution spy satellite? It just might work. Maybe I should mention that at the next funding request.

So far, I'd managed to avoid all the university gossip concerning Dr. Rialson's murder in his apartment three days ago. Even though he was a colleague in the applied physics and nuclear engineering department, and the department's expert on health physics (radiotherapy, that sort of stuff), I'd never had much to do with him.

Anyway, I didn't think about it any more until the cop returned to ask about the results of my check.

"Negative." At least that was quick.

He gave me his "I'm trying to be patient" look. I wasn't in the mood for it and went back to typing on the computer.

"What else could have caused his death? No one else can think of anything."

No one else? That put things into a slightly different light. Maybe I could give this a little thought. I have a reputation which I liked to enhance whenever possible.

How could you give someone a high rad dose without feeding them cobalt-60? It'd have to be done with a limited amount of material and equipment. It would also have to be quick.

"Any idea of the dose he got?" I asked.

"They're guessing around 15,000 rems of neutron exposure." Damn, he must have died within a few hours of getting exposed. That was incredible. But it could be done.

I led him to the vault containing the university's highly enriched radioactive isotopes. I grabbed an inventory list and slowly started to count off the plastic encased isotopes. They appeared to be all there, so I grabbed a radiac from a locker and started to examine the blocks more closely.

"About 30 years ago there was a really stupid scientist trying to demonstrate the principal of nuclear fission to some students by holding two blocks of uranium apart with a screwdriver. By allowing the two blocks to come closer together, the neutron count being measured would go up from the fission reactions. Well this guy's screwdriver slipped and the two blocks came completely together. Bam, the uranium formed a critical mass and blows apart, bombarding him with neutron radiation in the process. He died about 10 hours later."

"You think that could have happened here using two of these blocks."

"Yes, just as I thought, two of these are fake. To use them you'd have to rip the plastic and lead casing off. Since the casings are put on by machine, the killer probably couldn't put them back together right, so he switched them with these phonies."

Back in my office Detective Johnson finally understood enough to ask the obvious question, "This looks complicated and time consuming. Why bother? Why not just use a gun?"

Fortunately, I had the obvious answer. "For the pain. Radiation poisoning is a horrible way to die. I imagine about a half hour after being exposed he was feeling nauseous; diarrhea was probably next, then convulsions. A lot of the water in his body would break down into hydroxides, and internal bleeding begins. It just gets worse from there. Finally, I imagine he slipped into a coma and died, lying in his own vomit and crap." I smiled at the detective. "I'm sure he was in agony for around 10 hours. The only thing I'm having trouble understanding is how Rialson was held still while someone rigged up something to bring the two blocks together then pull them back apart. The killer had to be far away. What's more, he'd have to keep Rialson in his apartment until the radiation sickness incapacitated him."

"I think I can answer that." Was the detective going to surprise me? "Rialson was beaten up pretty badly, but not badly enough to kill him."

Then it was obvious. Why didn't he tell me that in the first place?

"Who has access to this locker?"

"Myself, the dean, three or four other scientists working in radiation, and . . . and Dr. Rialson's grad students." My face lit up.

"You think one of them might be responsible?"

"It's a possibility. Being a grad student in research can be frustrating. A lot of the professors will delay a student's graduation to get more cheap labor out of them."

"I see. And Rialson was barely forty and a big man. None of the other professors could beat him like that. And they would have access to him at his home. They might have been able to rig some kind of trap." Yes, he was sold. Excellent.

"Thanks for your help!" He rushed off, anxious to be away from me. Which was fine by me.

He'd taken the bait completely. If there was one thing I knew, it was that Rialson's three grad students hadn't killed him. One had just started and had no reason; the second was graduating at semester's end, so would also have no reason; and the third was, in my opinion, simply not bright enough for this scheme. Fortunately, Johnson didn't know this and would spend his time bugging him. Now I could find the real killer.

My theory was rather simple. It would just be a matter of research. I spent the rest of the day looking through papers Rialson had published in the scientific journals. I also looked at the dates and import of the papers.

Later that night, my theory was confirmed when I went through his office and read his recent notes. The police had already been there, of course, but they couldn't understand the notes, and what they told about the man.

Simply put, Dr. Rialson wasn't a particularly good scientist. Most of his previous papers had merely presented irrelevant experimental results with little insight, no new theories, no inventions. To advance at a university to an associate or full professorship, one had to publish or get grants. Rialson wasn't succeeding in either area.

If one of his colleagues had killed him, it would be for one of two reasons; somebody was stealing his research, or he was stealing someone else's. My study of his most recent work pointed me toward the latter. Unfortunately, none of his notes gave a clue as to exactly what that was.

I would just have to go to each of the professors that Rialson worked with and find out which one of them it was.

"Just curious Dr. Ahira. I've taken a break in my research for a couple of days and figured I'd see what you were up to. You do, after all, use my accelerator a great deal."

"The Dean will be happy to know you have obtained title to the accelerator."

Nuts. I did not get along with this guy. He turned back to his tray full of sapphires and started putting select ones into a metal can. Slow as a snail he chose from the pile of identical stones. I struggled to keep my temper in check.

"I am in charge of allocating time for the accelerator, as you well know. What with Defense International coming in next week to bombard computer chips, space could get tight. I have to prioritize use of the machine. Now tell me about these jewels, and how much time you need."

"The jewels are just ordinary rhinestones," he said, barely looking at me. "By bombarding them with the accelerator and using a special screening technique, I have been able to increase their hardness and give them this rich blue color." He held up one of the gems. It was a very nice ice-blue. "The process can be used for both commercial and industrial gems, and once I have the screening technique right, I'll be able to mass produce them with a much smaller accelerator."

I held one of the gems up to the light, "How much will it increase in value."

"Value is relative, sir, to supply and demand. Right now, about 20 times."

"Hmm, you may make some money off this one."

He gave me a look of self righteous contempt, "My interest is in gem structures, not money."

Right. Another one of those kind. I watched as he set up his device at the end of the accelerator. We walked out the exit together. One of the techs activated the door, and the six-foot-thick concrete slab shut behind us, to the ringing of the alert bells.

I followed him as he lunged ahead into the control booth, where the technicians were ready to start the machine, trying to lose me. "Hey," I called. He finally came to a stop at the booth door. "Weren't you working on this with Rialson."

"No, not really. He just helped with some special radiation monitoring equipment."

"Hmm." I turned to leave. This might be tougher than I'd thought.

"Dr. Peterson?"

"Yes?" I turned to look at him.

"I'll need five hours next week."

I flashed my toothiest smile at him. "You got'em sport." Time for the next suspect.

"Check."

Every time without fail it happens. I moved a pawn in front of my king. Every god damned time I came here he had this stupid chess board out. And he always insisted we play. He settled for the pawn. I broke out my rook to drive his queen back. I was beginning to hate this asinine game.

"Your research, sir."

"What was that?"

Don't pull that "My hearing aid isn't working right" jazz on me. "I said I need to know about your research. I'm trying to prioritize use of the accelerator for next week."

"Yes, Defense International, I'd almost forgotten." He leaned back in his easy chair, his rotund, old body becoming almost motionless. For a moment, his eyes started to glaze. One of these days the old goat's gonna fall asleep in front of me. It hasn't happened yet, but I'm waiting. Finally, "They're paying a huge rental aren't they?"

"Of course, sir. The department negotiates hard on these things."

"Right, hmm, check." He suddenly moved up his bishop. Damn! He'd conned me good with the senile bit.

Dr. Rubin was the oldest professor here, and the department emeritus. His specialty was radiochemistry, a field he'd practically pioneered. He was one of the few people I really respected. I sacrificed a knight to get out of check; now if I could just get this conversation moving.

"My research, now," he started. What luck, he was finally on the subject. "I've been working on an unstable chemical compound."

"What's so unusual about that."

"Its a "link-up" molecule. It can be attached to a variety of carbon-based compounds. The thing about it is that it breaks up with exposure to even a mild amount of radiation. The resulting chemical breaks down the compound it was linked to."

"Uh huh, it sounds fascinating. But what's the use of it?"

"C'mon boy, use your imagination! What if it were linked to pesticides? Spray it on a crop; then, after enough exposure to sunlight, the pesticide breaks down into simple, harmless compounds. A major environmental hazard gone, poof!"

That was good. Very good, as a matter of fact. If I had had any interest in chemistry, I'd have offered my help. But this wasn't getting me anywhere. I'd have to divert his attention, then slip in the big question. I started to make a series of rapid offensive moves with my Queen to distract him, while I put the pressure on.

"The cops were asking me about Rialson."

"Really?"

"They think it was radiation."

"Sort of ironic, almost."

I looked into his eyes to see if he was giving anything away, but he just seemed sad. "That's what I thought. Didn't know him very well myself. No reason. How 'bout you? Work with him any?"

"A little."

This was like pulling teeth. "Oh?" I tried to sound surprised.

"Yes, he helped with the radiation sources for the later experiments. I suppose I'll have to get Rogers' help, now."

He made a move with his queen. I realized I hadn't paid any attention to the effect of my moves on the game. "Checkmate. I can't see why you made that last series of moves."

"Wasn't thinking, I guess." I got up to leave. I hated to lose. One way or another, I'd figure this out.

I found Dr. Rogers on his hands and knees outside the radiophysics lab wiping the floor with a piece of filter paper.

"Can't you get a grad student to do that?" I asked him.

He unsteadily lifted himself up, placed the paper in a small tin container, and marked a number on the container and on a map of the building at the point corresponding to our location. Then he moved to another spot ten feet away to try again.

"It relaxes me."

"Have you ever found any unusual levels?" The papers, called swipes, would be measured for radioactivity. It was a good way to spot radioactive contamination.

"Last time was about five years ago. One of Rialson's . . . one of the grad students got sloppy." Rogers actually looked haggard. Always thin and gaunt, he seemed even more pale than usual. Of all the professors, Rogers, as the radiation expert, worked closest with Rialson. Maybe they had been friends, or maybe he felt guilty.

I followed him around as he continued taking swipes. God, what a waste of time.

"How have you been doing since Ri. . . since, you know?" I figured I might have to be tactful on this one.

"Not bad." Rogers was the youngest of the lot, younger even then Rialson. But I didn't think he could overpower Rialson either.

"Close friend?"

"Yes, he was." He looked at me; then his face became suspicious. "Why all the questions? What do you really care, anyway?"

I don't, you idiot. "I'm just trying to make small talk. You see, the cops have been asking me about Rialson's death. I'd wondered if they'd bothered you yet?"

"A little, just some basic questions."

"Who do you think would kill him?"

He became even more nervous than before. "I haven't the foggiest idea. I hadn't seen him much recently."

"You were doing research together."

"Well, a little."

"Hey, don't get defensive. I'm not the cops, remember."

"I'm not defensive." He forced himself to look annoyed at the thought.

"What kind of research were you two doing together? Are you going to be set back."

"Probably not. We were trying to devise a way to reduce the radiation dosage required to treat cancer patients on radiotherapy."

I did a double take; it was the first thing Rogers had ever said that impressed me. Depending on how successful they had been, this could be extremely big. The side effects of radiation treatment were substantial.

"How successful were you?" I asked.

He looked downcast. "Not very, yet."

Not yet. Could he be lying about that? We made it back to the lab with the radiation counting equipment. As he entered, he turned to wave goodbye and get rid of me. One last question first.

"How long before you know if you have anything?"

"I don't know. See you later." He turned and started to shut the door.

"Oh, one more thing." He stopped, annoyed. "Did the police tell you how Rialson died?"

"No, they didn't." He turned to look at me.

"Radiation poisoning. Think about it." I turned and left, smiling.

"None of them checked out?"

"No, none at all."

"Sorry detective, it was just a guess." I kept my face straight while I looked around Rialson's apartment. I'd convinced him to bring me here on the off chance I'd provide some clues to him. I had no intention of doing that, but perhaps I would get some answers for myself.

"After conducting a more detailed radiation survey, we believe the uranium blocks were placed right here." He pointed to a coffee table in the middle of the living room. "We think Rialson was beaten up over here." He pointed to a little dinette. "From everything we can find, it was done by only one guy. Rialson was then dragged to the sofa. The killer rigged up his device on the coffee table and left the room. After Rialson was exposed to the radiation, he came back in, took the device, and left. The coroner figures Rialson lay unconscious for about an hour. By the time he woke up, he was too sick to even call for help, just like you said."

I nodded. The question was still, how could someone at the university have beaten Rialson like that?

"Could Rialson have been drunk or drugged at the time?"

"The coroner says he could find no trace of alcohol or anything else like that. I thought of that as well."

Hurray for you. "What will you do now?"

"We'll keep our eyes open, but other than that there's nothing much we can do."

I looked at him and nodded, then turned away, hiding a smile. I knew how it was done and I knew who did it. It was brilliant, and so was I.

"So they've given up?"

"Yeah. They said they couldn't figure it out." I moved a pawn.

"That's too bad. I liked Rialson. Big, nice, unassuming guy." Rubens moved a knight.

"Really." I moved another pawn.

"Yes, he helped me quite a bit." The knight took my pawn.

"He helped himself to your research as well." I moved my bishop to counter his knight.

"What?" He looked at me in surprise, and got his knight out of the way.

"The hard part was trying to figure out how someone around here could beat Rialson up so badly." I took a pawn with the bishop.

"I don't see how it could be done, either." His hand faltered over a pawn before moving the knight again.

"Of course, the killer had to knock out Rialson long enough so that he would be too incapacitated from the radiation to go for help." I took his knight with my own.

Rubens grinned cagily. "That's a fascinating story." With a great show of calm, he moved a pawn to threaten my knight.

"Like I said though, I couldn't figure out how he could be beaten like that. The police, of course, went straight for Rialson's grad students. Then I got to thinking, what if that's what the killer wanted them to think? I mean, who would believe an old man could beat up Rialson?" I smiled back and took his pawn with my bishop. "Check."

His color was draining. "What are you saying?" He blocked the bishop with another pawn.

"I'm saying, what if the beating took place after he was already knocked out? What if the beating was just a ruse and he was really drugged? Something slipped in his drink perhaps? The coroner couldn't find any evidence of drugs; but then, who's invented a chemical that can break down a poison upon exposure to radiation?" My queen moved up to take the pawn. "Check."

"You're out of your mind." He blocked my queen with his remaining knight.

I took the knight with my queen. "I'm sure, though, that they can find evidence of the drug once they know exactly what breakdown products to look for."

He fumbled with the pieces. I set them up again while he put his head in his hands and started to weep. After a long moment he looked up at me. "This isn't the first time this has happened to me. Forty years ago I had another big one. My boss stole it from me. He just took it from me. There wasn't anything I could do, though. I was here on a doctored-up work visa, as part of the CIA's cold war effort, but I still had to keep a low profile. As an ex-NAZI scientist, I was lucky to have been let in the country when the war ended. That's what he told me, when he walked away with my life's work. I vowed it would never happen again." I looked into his eyes. I understood.

"I wanted him to pay, like that other man should have paid. I spent forty years devising that scheme. Forty years. I'm old now, I have nothing to lose." He tried to take my bishop with his king.

"Uh, uh. You can't move into check." I pointed to my queen.

"What are you going to do? Turn me in? Or do you really care? Is this just another game to you?"

"I thought about letting you go. Rialson doesn't mean anything to me. But you are the only scientist here whose reputation matches my own. The gain to my own prestige is too great to let go."

"I understand." He looked at the board to figure out his next move.

"Don't bother; I'll win in four moves." I saw his hand reaching into his desk drawer. I sighed. Had he come to this? "Dr. Rubens," I said softly, "go out with dignity. I'm forty years younger than you. If you reach for that gun, I'm going to have to break your arm."

He looked at me for a long moment, then he closed the drawer and slumped into his chair.