Curt watched the hand on his oxygen gauge drop lower and lower. There could be no turning back now! If they didn't find Landreth's ship within the next hour.... Rikert spoke, worry creeping into his voice. "We ought to be getting close, Emmons! How about using a signal flare?" Curt peered ahead at the cobalt sky. The horizon dropped sheerly away. He shook his head. "Only got two flares, can't waste them! Wait 'til we sight the mountains." Rikert grumbled, but Curt saved his breath. Half an hour later they glimpsed a serrated line of cliffs low on the horizon. Curt released one of the flares in that direction. They watched it rage in a fiery arc across the darkness for perhaps twenty seconds ... then it disappeared. They awaited an answering signal. Anything to guide them! But nothing appeared. The darkness pressed in, almost tangible. Despair washed over Curt like a cold wave from the sea. "Better set your oxygen flow to one-half," he advised. They hurried the pace now, heedless of sharp rocks and dangerous gullies. Once Curt pulled Kueelo back from a steep brink just in time. The little Martian was staggering. Could Landreth have given up hope on them, and hoisted gravs? At the thought, Curt hurriedly brought out the remaining flare. With a prayer on his lips he aimed it, this time in a higher arc. Then Kueelo was clutching at Curt's arm, pointing far off to the left. There was the answering signal--a thin pencil of light slicing upward. It flashed on and off at intervals, but it seemed a long way! Already, sharp pains were slicing through Curt's lungs. He stayed close to Kueelo--but the Martian's fatigue seemed to have left him now! He was giving voice again to the peculiar little aria in the higher octaves which Curt had come to know so well. In that strange tune was a challenge, a promise--and something more. It was pagan. It was strength. It got into a man's soul! It seemed an eternity. They were nearing the cliffs, stumbling into a rocky ravine. They saw the spaceship, Landreth's ship! But the scalpels of fire in Curt's lungs were unendurable. The spaceship and all the terrain danced and faded away. His legs were leaden, Kueelo staggered against him, and somehow he managed to hold the little Martian upright. A vague impression ... a spilled square of light out of which a helmeted figure came leaping. Kueelo collapsed, sliding slowly away. Curt plummeted forward, gasped for air where there was suddenly none, then utter darkness claimed him. III There was air now. Great gulps of it. Someone had thrown back Curt's helmet, and he could hear the steady thrum of the airostat. It was beautiful music. Kueelo had recovered, and Rikert. And a fourth man was there. As Curt came to his feet he heard Rikert's voice, a little suspicious, addressing the stranger. "You! You're not Landreth. I thought we were going to meet--"