He had not progressed far--in the dark the uncertain footing was dangerous--when the breeze, sighing down the canyon with cool mountain-top air for the hot plain, brought confirmation of his fear with it. A whiff of strange odor that stung in his nostrils and tickled his windpipe harshly. Then his eyes began to smart as it grew rapidly stronger; the gas the buzzards had used to blanket the mesa was a dense one, designed to seek out the aero people in the depths of their underground fortress. Torcred halted, blinking, struggling with the growing need to cough. He recognized the odor after a moment--the same poison that the machines called skunks used against their enemies. He knew that enough of it was deadly. And a cold hand of terror clutched at his heart. * * * * * He flung caution from him and started to scramble recklessly, planlessly upward. Denser clouds of gas met him, and, half-blinded, he stumbled against sharp rocks and almost fell when fits of coughing shook him. His chest became a rasping furnace, and each deep panting breath was a flame. Bitterly he knew that his will could not drive him much longer into that torment.... In the air something flew burning, and the light of its destruction fell bright as day into the canyon and threw shifting shadows. Torcred's tear-filled eyes blurred the glare, but he glimpsed a small dark-clad figure huddled on the rocks not ten feet from him, across a black crevice that might be five or fifty feet deep. He crouched and sprang; weakened knees betrayed him, he landed clawing on the rounded lip of the chasm and barely managed to pull himself up to the girl's side. But new strength steeled him as he gathered his feet under him and dragged both her and himself erect. Ladna was alive and conscious; she leaned against him, coughing weakly. "I was coming back," she gasped in his ear. "I'd have been up there ... but I was coming back ... to you...." Torcred hardly understood her. "Come on!" he croaked. "Down!" The way seemed immeasurably longer than the way up had been. It was really a little longer--the gas was settling fast--until, staggering, each half-supporting the other, they reached a level where the air was no longer choking poison. Ladna grew able to stand alone; swaying a little, she followed Torcred down the treacherous slides in the canyon's mouth. On the soft wind-piled sand below the great rifted rock, where Torcred had last seen the visionary stranger, they sank down to rest by common consent. Torcred listened anxiously to the girl's hoarse breathing. He moistened his lips and asked, "How do you feel?" Ladna stirred and sat up with an effort that set her coughing again. "I'll be all right.... We'll go back into the desert, and live there somehow, as long--as long as we live." "That's right," said Torcred. In the dark she couldn't see how his face grew grim at the thought of how short their life together was likely to be.