The pack was not twenty feet away when Allan reached the stair door. He slammed it behind him, heard the latch click. He mounted the narrow, winding steps with the last dregs of energy draining from him, and heard a crash below that told of the collapse of the barrier. But he had reached his plane, had flung the girl into it, and was pulling himself in when the first of the pursuers burst out on the roof. Allan thrust home the throttle, the helio-vanes whined, and his 'copter leaped skyward. He glimpsed men running across the roof; they vanished behind a leafy arbor. Dane turned the nose of his craft toward Sugar Loaf, amethyst in the haze of distance, but from that green arch a black aircraft zoomed up and shot after him. The American shook his head free of the cobwebs of fatigue, and veered westward. He must not lead the Easterners to Anthony's refuge. Through the dead air, over a dead world they shot--Allan's white flier and the ebony plane with the bloody emblem of the seven-pointed star emblazoned on its nose. Allan wheeled again as the pursuers reached his level on a long, climbing slant. But they continued rising! They, were five hundred, a thousand feet above him. Then they leveled out, and dived down. Their strategy flashed on him--they were planning to shepherd Dane down, to force him to land where they would have him at their mercy. And their craft was the faster! * * * * * The black ship was right on his tail; Allan flicked his controls and his 'copter slid sidewise on one wing. The other plane banked in a tight arc and sped for him; Dane countered with a lightning loop that brought him behind his enemy. His gray eyes were steel-hard, his lips were a straight, thin gash. The other ship was faster, but his, lighter and smaller, was more flexible. He could not get away, but--They flipped up and back in an inside loop; Allan's little craft barrel-rolled from under. This sort of thing could not last forever. With each maneuver he was losing altitude. Serrated roof-tops were already a scant fifteen hundred feet beneath him, gaunt gray fingers that reached up to pluck him from the sky. Only half Allan's mind was concentrated on the aerial acrobatics. The other half plodded a weary treadmill. In the nullite chamber beneath Sugar Loaf's summit, he thought, were three couples whose knowledge and wisdom had preserved them for the repeopling of the Earth. Their children, and their children's children--starting from such a source what heights might not the new race attain?