Riordan did not look closely at the tower. It was a crumbling stump atop a rusty hill, unhuman and grotesque. Once, perhaps ten thousand years ago, the Martians had had a civilization of sorts, cities and agriculture and a neolithic technology. But according to their own traditions they had achieved a union or symbiosis with the wild life of the planet and had abandoned such mechanical aids as unnecessary. Riordan snorted. The hound bayed again. The noise seemed to hang eerily in the still, cold air; to shiver from cliff and crag and die reluctantly under the enormous silence. But it was a bugle call, a haughty challenge to a world grown old--stand aside, make way, here comes the conqueror! The animal suddenly loped forward. He had a scent. Riordan swung into a long, easy low-gravity stride. His eyes gleamed like green ice. The hunt was begun! * * * * * Breath sobbed in Kreega's lungs, hard and quick and raw. His legs felt weak and heavy, and the thudding of his heart seemed to shake his whole body. Still he ran, while the frightful clamor rose behind him and the padding of feet grew ever nearer. Leaping, twisting, bounding from crag to crag, sliding down shaly ravines and slipping through clumps of trees, Kreega fled. The hound was behind him and the hawk soaring overhead. In a day and a night they had driven him to this, running like a crazed leaper with death baying at his heels--he had not imagined a human could move so fast or with such endurance. The desert fought for him; the plants with their queer blind life that no Earthling would ever understand were on his side. Their thorny branches twisted away as he darted through and then came back to rake the flanks of the hound, slow him--but they could not stop his brutal rush. He ripped past their strengthless clutching fingers and yammered on the trail of the Martian. The human was toiling a good mile behind, but showed no sign of tiring. Still Kreega ran. He had to reach the cliff edge before the hunter saw him through his rifle sights--had to, had to, and the hound was snarling a yard behind now. Up the long slope he went. The hawk fluttered, striking at him, seeking to lay beak and talons in his head. He batted at the creature with his spear and dodged around a tree. The tree snaked out a branch from which the hound rebounded, yelling till the rocks rang. The Martian burst onto the edge of the cliff. It fell sheer to the canyon floor, five hundred feet of iron-streaked rock tumbling into windy depths. Beyond, the lowering sun glared in his eyes. He paused only an instant, etched black against the sky, a perfect shot if the human should come into view, and then he sprang over the edge.