"You mean the alien was gone," Dr. Weeve contradicted him.
Engel's throat went dry and he stared at them.
"An alien!" shouted Marston. "Don't you understand?"
Dr. Weeve smiled thinly. "Mr. Engel's curious to learn the latest about them and would draw us out in this childish way. I assure you we despise them far more than millions who only read about them in their daily telescripts. Since the flying saucer crash in '68, we've been very much aware of their close surveillance of this world."
The doctor's face clouded as he gazed at the city. "The filthy blue spawn of Centauri send us exceedingly clever spies. Before invading our cities, they must seek out our military installations and plant explosives at key points. Their assassins must be ready to strike...."
Dr. Weeve gently wrung bony hands, and Marston leaned forward, his pale jowls quivering angrily. "To safeguard public welfare, this city branch of Alien Detection must find and exterminate aliens. So far we can boast of a perfect record, thanks to the new detection screen."
Aliens? Engel winced, recalling the mournful little stranger. "I can't believe that he--"
"That he's a humanoid?" Marston spat out the word as if it were a lump of vileness in his throat. "C. G.'s a sneaking saboteur who conceals his ugly blue hide under a layer of false skin! But he's been detected."
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."