"Amos also had a master's degree in electrical engineering, and he left us an interesting device: a black box that locates telepaths."

"Amos also had a master's degree in electrical engineering, and he left us an interesting device: a black box that locates telepaths."

I gestured to Rob. "We don't know yet," he said. "Most of the electronics are perfectly straightforward, but there are two components that Amos apparently made himself. They're the heart of the finder-and we still don't know how they work."

"Interesting," Green murmured. He looked at me. "May I see them?"

"Sure. The workroom's in the basement; the stairs are around that way."

I let Rob lead the way downstairs, bringing up the rear myself. Green, I noticed with grim amusement, practically walked on Rob's heels in an effort to stay as far away from me as possible.

I'd only lived in the house for about five months, having moved in just after my return from California with the telepath finder, and the basement thus hadn't had nearly enough time to fill up with ordinary homeowners' junk. That was just as well, because with the workbench and electronic gear Rob had brought in the place was already pretty crowded. In the center of the table, wired to an oscilloscope, was a crab-apple-sized lump of metal.

"That's one of them," Rob said, pointing it out. "We've got seven-Amos left us eight but I ruined one getting it open."

Green stepped over to the table and carefully picked up the sphere. "Heavy," he grunted. "What'd you find inside?"

"A couple of commercial IC chips, an inductor coil he apparently wound himself, and some components that unfortunately were connected somehow to the inside of the shell and which I ruined when I cut it open. But we've got lots of data on its characteristics."

Rob pulled over a fat lab notebook and within ten seconds the two of them were embroiled in a technical discussion about six miles over my head. I didn't even bother to try and follow it; I was more interested in learning as much about Green as I reasonably could. Moving to within two or three feet would have given me complete access to both his surface thoughts and a lot of the stuff underneath, but he was keeping me in the corner of his eye, and I didn't want to push him too hard. So instead I kept my distance and worked on picking up the high points of his personality.

He wasn't going to be as easy to get along with as Rob had been; that much was obvious right from the start. Along with his manipulative tendencies, Green had more than his fair share of egotism, ambition, and something I took to be contempt for people he considered inferior to himself. But he seemed smart enough, if the speed at which he assimilated Rob's pages of numbers and graphs was any indication, and Rob at least seemed to think he could be trusted to keep my secret. If he was willing to work for the pittance I could afford to pay, I decided at last, the job was his. His personality I could live with or stay clear of.

After a while Rob ran out of words, and Green turned back to me. "I think I understand," he said. "These kernel things apparently act as antennas for whatever it is you guys broadcast, covering a broad enough spectrum to pick up all of you and plot a resultant. I gather that it works; so what do you need me for?"

"I want you to use those-kernels," I said, adopting his term for Amos's gadgets, "to design and build something entirely different. You'd be working mainly for the challenge of it, though; I can't afford to pay you much."

"I want you to use those-kernels," I said, adopting his term for Amos's gadgets, "to design and build something entirely different. You'd be working mainly for the challenge of it, though; I can't afford to pay you much."

"More or less. Having known Rob for the past four years helped, too. All right. What I want is a device that'll block my telepathic ability."

Green frowned. "You mean like something to make the broadcast directional?"

"No-something to kill it altogether, the way a copper shell around a radio transmitter will absorb the signal."

"But why would you want-" He broke off, having answered his own question with impressive speed and accuracy, even given that my long-distance romance with Colleen was reasonably well known.

"Temporary blocking, I assume?"

"Right." Though there were times I'd wished to be rid of the damn talent permanently. "When do you want to start?"

"I haven't said yet I'd take the job," he said, a bit testily. I hadn't been wrong earlier; he didn't much like having his mind read.

Rob, as usual, saw the humorous side of his friend's reaction and chuckled. Green flashed him an annoyed look, then managed a wry smile. "Right-I don't have to say things like that here, do I? Okay.

How about if I come in Saturday morning-say around eight-thirty?"

"Sounds fine. I'll see you then."

I leaned against the front door for a minute after I let them out, feeling the contacts fade as they walked to the street and Green's car. I knew I should be happy I'd found a replacement for Rob so quickly; it was only a week ago that he'd realized how much preparation his upcoming prelims were going to take. And yet, despite Green's apparent qualifications, there was something about him that made me uneasy.

There'd been something going on beneath the level I could read, something... sinister was far too harsh a word; maybe opportunistic fitted the sense of the feeling better. I probably should insist on a deeper probe into Green's mind before I let him examine Amos's devices further, a part of me realized. But my pragmatic side quickly scotched that idea. As long as he made me a telepathy shield it was a matter of supreme indifference to me what kind of schemes his ambitious little mind might be hatching.

Sighing, I pushed away from the door and headed back to the living room. Patience is a virtue, I told myself firmly. Flopping down on the couch, I put it carefully out of my mind and reached out. Colleen?

I'm here, Dale, her answer came immediately.

We talked for a long time, and the afternoon shadows were cutting sharply across my minuscule lawn by the time we broke contact. Spending time with Colleen invariably improved my mood, and I was sorely tempted to ignore my psychologist's standing order and pretend the latest daymare simply hadn't happened. But reason eventually prevailed. Hauling the vision out of my memory, I went over it with a fine-tooth comb. By the time I finished I was depressed again, a mood I'd had to put up with a lot lately-Nelson had always been the melancholy sort.

Whatever other qualities Green might or might not have possessed, I had to give him full credit for punctuality; he arrived on Saturday at eight-twenty-five sharp. I took him downstairs and spent nearly half an hour showing him where all the equipment and supplies were. He still tended to shy away from close contact with me, but since his personality hadn't changed markedly in the past two days such avoidance was mutually agreeable.

"So what are you going to do first?" I asked when I'd finished the grand tour.

"Double-check some of Rob's numbers," he said, pulling an ancient wave generator over toward the center of the table. "I want to see if flipping polarity on any of the kernel's bias terminals will affect the output the way he said it does."

I pulled a chair over to the far end of the work bench and sat down, resisting the urge to suggest that would be a waste of time. He already thought I was too impatient. "What will that tell you?" I asked instead, trying to sound merely curious.

"It'll tell me if energy is disappearing into the thing-if so, it may be acting as a transmitter instead of a receiver. Your shield might consist of one or more of these things blasting out an interference signal."

"Wouldn't it be easier to absorb the telepathic signals instead?" I suggested. "Then you could use them as receivers, the way they're designed."