nodded. "So?"

"So," Donegan said, "we've got to convince Fredericks' friends—the unbalanced fringe—that we are supermen, that we have no limits, that no matter what they try against us they're bound to fail."

"Nice trick," he said sourly.

"Very nice," Donegan said. "And what's more, it works. Nobody except an out-and-out psychotic commits a crime when he hasn't got a hope of success. And these people aren't psychotics; most criminals aren't. Show them they can't get away with a thing—show them we're infallible, all-knowing, all-powerful supermen—and they'll be scared off trying anything."

"But killing Fredericks would do that just as well—" he began.

Donegan shook his head. "Now, hold on," he said. "You're getting all worked up about this. It's your first time with this stakeout business, that's all. But you can't kill him. You can't kill except when really necessary. You know that."

"All right. But if he's going to kill me—"

"That doesn't make it necessary, not this time," Donegan said. "This vengeance syndrome doesn't last forever, you know. Block it, and you're through with it. And think how much more effective it is, letting Fredericks go back alive to tell the tale."

"Think how much more effective it would be," he said, "if Fredericks managed to get me."

"He won't," Donegan said.

"But without weapons—"

"No Psi Operative carries weapons," Donegan said. "We don't need them. We're supermen ... remember?"

He twisted his face with a smile. "Easy for you to talk about it," he said. "But I'm going to have to go out and face it—"

"We've all faced it," Donegan said. "When I was an Operative I went through it, too. It's part of the job."

"But—"

"And I'm not going to tell you how to do the job," Donegan went on firmly. "Either you know that by now, or you don't belong here."

He got up to leave, slowly. "It's a fine way to find out," he said mournfully.

Donegan rose, too. "Good luck," he said. And meant it, too.

That was the chief for you, he thought. Send you out into God knows what with no weapons, no instructions, lots of help planted for the man who wanted to kill you—and then wish you good luck at the end of it.

Sometimes he wondered why he didn't go in for some nice, peaceful job of work—like rocket testing, for instance.

redericks, downstairs, was deciding to do things the subtle way. The man upstairs—Jones, Brady or whatever his name was—deserved what he was going to get. Psi powers were all very well, but there were defenses against them. Briefly he thought of the man who'd sold him the special equipment, and wondered why more criminals didn't know the equipment existed. It worked; he was sure of that. Fredericks knew enough of general psi theory to know when somebody was handing him a snow job. And the equipment was no snow job.

A force shield, that was the basic thing. A shield with no points of entrance for anything larger than air molecules. Sight and sound could get through, because the shield was constructed to allow selected vibrations and frequencies. But no psi force could crack the shield.

Fredericks has sat through a long explanation. Psi wasn't a physical force; it was more like the application of a mental "set," in the mathematical sense, to the existing order. But it could be detected by specially built instruments—and a shield could be set up behind which no detection was possible. It wasn't accurate to say that a psi force was blocked by the shield; no construct can block that which has no real physical existence. It was, more simply, that the shield created a framework inside of which the universe existed in the absence of psi.

That wasn't very clear, either, Fredericks thought; but mathematics was the only adequate language for talking about