The body struck the cover and knocked it aside. The alien shoved it a bit higher, and it quivered as the swords above pierced it. He dropped the dead carcass and sprinted forward. He had bought all the time he could, and there was nothing for him to do now except try to reach the end of the tunnel before the gas overcame him. His head was held high as he ran--he had deduced that they had to use a heavier-than-air gas. He did not have far to go. He reached the end of the tunnel and stumbled onto a conduit leading from the main air compressor. For a short time he lay sprawled across the metal duct, too exhausted to move. Finally he raised his head and looked wearily about him. He spied a vent opening on a level with his head, and with a determined effort he removed the screen and climbed through. Utter fatigue showed in line of his body. Outside he stood for several minutes, drawing clean air deep into his lungs. There were no sentries here. They had not expected him to get this far. But they would come, soon after they failed to flush him from the tunnel. The alien looked about, then headed unerringly toward the sand banked against the wall of the pumping station. He dug until he had made a long hollow then let his weary body fall into the shallow place and began piling sand over his legs. When he had covered all of himself except one arm, he burrowed it down until he was completely hidden from sight. "How can such a man be stopped?" Srtes asked. His face was drawn and gray, as though he had suffered some great defeat. * * * * * The alien must have dropped off to sleep for he stayed in the sand for several hours, and did not emerge until shortly before day-light. Evidently he had first made an opening through which to observe, for there were no guards about when he stood up and shook the sand from his body. He must also have studied all his surroundings. He had reached the city's end. The wall ahead of him was without a gate. He had been sent on a foredoomed errand. Though I had been acting under orders, I felt a kind of shame at the part I had played in the deception. Even then, however, he was not defeated. He struck out without delay to his right where there were few sentries, using his rooftop technique when needed, and reached a side gate within an hour. He dispatched the final sentry by dropping on him from a convenient balcony--he was probably too exhausted to risk a fight--and let himself out through the gate. He walked with jaded steps back the way he had come, skirting the outside wall closely. At last he reached the meadow for which he had started seven hours earlier.