For hours the hard-pressed beast had fled across the Martian desert with its dark rider. Now it was spent. It faltered and broke stride, and when the rider cursed and dug his heels into the scaly sides, the brute only turned its head and hissed at him. It stumbled on a few more paces into the lee of a sandhill, and there it stopped, crouching down in the dust. The man dismounted. The creature's eyes burned like green lamps in the light of the little moons, and he knew that it was no use trying to urge it on. He looked back, the way he had come. In the distance there were four black shadows grouped together in the barren emptiness. They were running fast. In a few minutes they would be upon him. He stood still, thinking what he should do next. Ahead, far ahead, was a low ridge, and beyond the ridge lay Valkis and safety, but he could never make it now. Off to his right, a lonely tor stood up out of the blowing sand. There were tumbled rocks at its foot. "They tried to run me down in the open," he thought. "But here, by the Nine Hells, they'll have to work for it! "