Malone sighed. He fished in his pocket for a pack of cigarettes, found one, and extracted a single cigarette. He stuck it in his mouth and started fishing in various pockets for his lighter. He sighed again. He preferred cigars, a habit he'd acquired from the days when he'd filched them from his father's cigar case, but his mental picture of the fearless and alert young FBI agent didn't include a cigar. Somehow, remembering his father as neither fearless nor, exactly, alert--anyway, not the way the movies and the TV screens liked to picture the words--he had the impression that cigars looked out of place on FBI agents. And it was, in any case, a small sacrifice to make. He found his lighter and shielded it from the brisk wind. He looked out over water at the Jefferson Memorial, and was surprised that he'd managed to walk as far as he had. Then he stopped thinking about walking, and took a puff of his cigarette, and forced himself to think about the job in hand. Naturally, the Westinghouse gadget had been declared Ultra Top Secret as soon as it had been worked out. Virtually everything was, these days. And the whole group involved in the machine and its workings had been transferred without delay to the United States Laboratories out in Yucca Flats, Nevada. Out there in the desert, there just wasn't much to do, Malone supposed, except to play with the machine. And, of course, look at the scenery. But when you've seen one desert, Malone thought confusedly, you've seen them all. So, the scientists ran experiments on the machine, and they made a discovery of a kind they hadn't been looking for. Somebody, they discovered, was picking the brains of the scientists there. Not the brains of the people working with the telepathy machine. And not the brains of the people working on the several other Earth-limited projects at Yucca Flats. They'd been reading the minds of some of the scientists working on the new and highly classified non-rocket space drive. In other words, the Yucca Flats plant was infested with a telepathic spy. And how do you go about finding a telepath? Malone sighed. Spies that got information in any of the usual ways were tough enough to locate. A telepathic spy was a lot tougher proposition. Well, one thing about Andrew J. Burris--he had an answer for everything. Malone thought of what his chief had said: "It takes a thief to catch a thief. And if the Westinghouse machine won't locate a telepathic spy, I know what will." "What?" Malone had asked. "It's simple," Burris had said. "Another telepath. There has to be one around somewhere. Westinghouse _did_ have one, after all, and the Russians _still_ have one. Malone, that's your job: go out and find me a telepath." Burris had an answer for everything, all right, Malone thought. But he couldn't see where the answer did him very much good. After all, if it takes a telepath to catch a telepath, how do you catch the telepath you're going to use to catch the first telepath?