Sheltering from wind-driven sand under the cover of a great monolith, Newlin and Songeen watched the racing figures of pursuit top the crest of the opposite ridge and start down. Man and girl were too winded and weak even to get up. They dared rest only a moment, then plunged on into the maze of tumbled ruins. Ultimate exertion had taken toll of their energies and rapidly burned up air reserves. Both were cruelly thirsty. The heat, even inside their insulated suits, was stifling. There was no time to take stock of manifold discomforts. The race was neck and neck. Death sniffed at their heels in the guise of mechanical trackers. On Venus, life is to the swift and cunning. To Newlin, life was perilous, but sweet. Their helmet microphones picked up and amplified a curious droning buzz. It was the deathsong of the electronic tracker and it seemed closer than it was. Slowly, inexorably, it grew louder. Sound swelled steadily, and it was a whiplash to their flagging energies. They fled in panic through the streets of the dead city. It was no real refuge to them, but its megalithic precincts gave some lying illusion of safety. They chose a twisting, tangled route into the very heart of the ruined city, with the instinct of a hunted animal to confuse its trail. They doubled back to cross their own trail twice, in the vain hope of baffling the electronic enemy. Newlin had been hunted before, on Mars, but by live bloodhounds. Pepper, oil of mustard, and perfumes had saved him then. But this hound followed not scent, but something intangible, electrical, and as mysterious as the soul-aura itself. It sorted two life-complexes from all other impulses and followed its own prime-directive--hunt down and kill. The end was inevitable as death. * * * * * Newlin laid ambush for the mechanical monster. Crouched in a nest of rubble, he waited for it, blaster gun ready. Around a corner of shattered stones, it appeared. It moved like a whipping shadow, like part of the gathering twilight. Silent, save for the high, nerve-tearing drone, it came warily across the courtyard paved with eroded stone. It was low, not animal in appearance, with the form of a fat, ugly snake. Fading light of the Venusian day cast a glint of metallic gray from its scaling of interlocked rings. Newlin waited for a close shot. How vulnerable was such a soul-less, mechanical monster to even the shattering-heat-forces of a blaster gun? Songeen lay quietly beside him, her body quivering as much from strained muscles as from fear. Behind the face-mask, her thin features were pale, ghostlike. With elaborate caution, the tracker circled their hiding place. Its froglike head, with a ruff of exposed filaments lifted, like an animal scenting blood. It edged slowly closer, its movement a glide, sinuous, crafty, with no suggestion of mechanical action.