Calhoun cleaned the paint gun. He was meticulous about it. He filled its tank with dextrethyl brought down from the laboratory. He piled the empty containers out of sight. "This trick," he observed, as he picked up the paint gun again, "was devised to be used on a poor devil of a lunatic who carried a bomb in his pocket for protection against imaginary assassins. It would have devastated a quarter-mile circle, so he had to be handled gently." He patted his pockets. He nodded. "Now we go hunting--with an oversized atomizer loaded with dextrethyl. I've polysulfate and an injector to secure each specimen I knock over. Not too good, eh? But if I have to use a blaster I'll have failed." He looked out a window at the sky. It was now late afternoon. He went back to the gate to the service road. He went out and piously closed it behind him. On foot, with many references to the photomaps, he began to find his way toward the landing grid. It ought to be something like the center of the invaders' location. * * * * * It was dark when he climbed other service stairs from the cellar of another building. This was the communications center of the city. It had been the key to the mopping-up process the invaders began on landing. Its call board would show which apartments had communicators in use. When such a call showed, a murder-party could be sent to take care of the caller. Even after the first night, some individual isolated folk might remain--perhaps unaware of what went on. So there would be somebody on watch, just in case a dying man called for the solace of a human voice while still he lived. There was a man on watch. Calhoun saw a lighted room. Paint gun at the ready, he moved very silently toward it. Murgatroyd padded faithfully behind him. Outside the door, Calhoun adjusted his curious weapon. He entered. There was a man nodding in a chair before the lifeless board. When Calhoun entered he raised his head and yawned. He turned. Calhoun sprayed him with smoke rings--vortex rings. But the rings were spinning fissiles of vaporized dextrethyl--that anaesthetic developed from ethyl chloride some two hundred years before, and not yet bettered for its special uses. One of its properties was that the faintest whiff of its odor produced a reflex impulse to gasp. A second property was that--like the ancient ethyl chloride--it was the quickest-acting anaesthetic known. The man by the call board saw Calhoun. His nostrils caught the odor of dextrethyl. He gasped. He fell unconscious. Calhoun waited patiently until the dextrethyl was out of the way. It was almost unique among vapors in that at room temperature it was lighter than air. It rose toward the ceiling. Calhoun moved forward, brought out the polysulfate injector, and bent over the unconscious man. He did not touch him otherwise. He turned and walked out of the room with Murgatroyd piously marching behind him. Outside, Calhoun said: