"Some things," Boyd said carefully, "are more possible than others."
"Thank you, Charles W. Aristotle," Malone said. "I hope you realize what you've done, picking up those three men. We might have been able to get some good lines on them, if you'd left them where they were."
There is an old story about a general who went on an inspection tour of the front during World War I, and, putting his head incautiously up out of a trench, was narrowly missed by a sniper's bullet. He turned to a nearby sergeant and bellowed: "Get that sniper!"
"Oh, we've got him spotted, sir," the sergeant said. "He's been there for six days now."
"Well, then," the general said, "why don't you blast him out of there?"
"Well, sir, it's this way," the sergeant explained. "He's fired about sixty rounds since he's been out there, and he hasn't hit anything yet. We're afraid if we get rid of him they'll put up somebody who can shoot."
This was standard FBI policy when dealing with minor spies. A great many had been spotted, including four in the Department of Fisheries. But known spies are easier to keep track of than unknown ones. And, as long as they're allowed to think they haven't been spotted, they may lead the way to other spies or spy networks.
"I thought it was worth the risk," Boyd said. "After all, if they have something to do with the case—"
"But they don't," Malone said.
Boyd exploded, "Let me find out for myself, will you? You're spoiling all the fun."