"He's detected?" Engel gasped. Dr. Weeve inclined his vulture-like head quizzically. "For an intelligent man, Mr. Engel, you seem rather poorly informed." He reached to a cabinet, and across a cathode ray screen trembled a narrow ribbon of light. "As you know," he said, "every act of an organism is preceded by an attitude, and that attitude takes the form of electromagnetic brain waves. The detection screen is quite simple. Sensitive electronic devices under the city dome pick up, amplify, and transmit brain waves to the central control here. Deviations from the social norm-wave are promptly investigated." * * * * * He ran a gnarled finger along the ribbon of light. "Note the low, rhythmic pulsations of the norm-wave--a happy citizen at a social task somewhere in the city." He adjusted a dial, and on the screen flashed a spasmodically twitching band. "A variation of anti-social type three--a citizen planning murder. Criminal Detection has a police detail observing him, and before he can strike, they'll take him in custody. Now C. G., the pseudo-man we're having shadowed." A jagged white band leaped in a wild dance. "Even cerebral abnormalities don't register this violently," the doctor said. "The electrical impulses of his artificial brain are powerful. The detectors easily penetrate his feeble brain shield. He thinks he moves unnoticed on his evil mission--but look at his tremendous pent-up hatred and fear!" Engel stiffened, his palms moist with sweat. C. G. was somewhere in this city of the future. Of course he was feeling terrified--but these witch-hunters were mistaking that terror for something else! He choked at a sudden thought. Why hadn't they discovered his own fear yet? Was his head injury somehow protecting him from their sensitive machines? Dr. Weeve was regarding him stonily. "Ingenious!" Engel blurted out. Marston placed an automatic on his desk and beside it a box of shells. "Yes, ingenious," he said, grinning, "but luckily for me these gadgets can't do everything. Trapping the alien is next, and that's my department. Show him the Tracer Room, doctor." Nervously trailing Dr. Weeve, Engel went to a steel door and peered through a window. For a moment it seemed as if he were high above the twinkling lights of a city at night until he made out a dark, sunken room and skeletal figures with earphones clamped to their long heads. They bent over a flat surface illuminated with bright grid lines and sprinkled over with a myriad glowing dots. Gaunt shadowy faces were fixed on a pip of light. "They place him on the east side of Baxter Avenue between 43rd and 44th streets," Dr. Weeve explained. He rubbed a lean jaw, frowning. "But how the detectors failed to pick up his presence before he reached the civic center baffles us. Seems as if he just popped up there." "I'm ready for the kill, gentlemen!" crowed Marston, slapping the holster strapped to his side. "You look pretty impressed, Engel."