They moved slowly across the ashy floor of the crater, occasionally circling small knolls or jagged rock outcroppings. Despite the cumbersome suits and the burden of the extra oxygen cylinder each carried, they made good time. Crag led the way with Larkwell close behind, threading his way toward the spot where the enemy rocket had fallen from the sky. They had to stop several times to rest and regulate their temperature controls. Despite the protective garments they were soon sweating and panting, gasping for breath with the feeling of suffocation. Crag felt the water trickling down his body in rivulets and began to itch, a sensation that was almost a pain. "It's not going to be a picnic," Larkwell complained. His voice sounded exhausted in the earphones. Crag grunted without answering. His feet ploughed up little spurts of dust which fell as quickly as they rose. Like water dropping, he thought. He wondered how long they would be able to endure the heat. Could they possibly adapt their bodies to such an environment? What of the cold of night? The questions bothered him. He tried to visualize what it would be like to plunge from boiling day to the bitterly cold night within the space of moments. Would they be able to take it? He grinned to himself. They'd find out! At the next halt they looked back at the Aztec. "We don't seem to be getting anywhere," Larkwell observed. Crag contemplated the rocket. He was right. The ship seemed almost as large and clear as ever. "Your eyes trick you," he said. "It's just another thing we'll have to get used to." He let his eyes linger on the plain. It was washed with a brilliant light which even their glare shields didn't diminish. Each rock, each outcrop cast long black shadows--black silhouettes against the white ash. There were no grays, no intermediate shades. Everything was either black or white. His eyes began to ache and he turned them from the scene. He nodded at Larkwell and resumed his trek. He was trudging head down when he suddenly stopped. A chasm yawned at his feet. "Mighty wide," Larkwell observed, coming up. "Yeah," said Crag, indecisively. The rift was about twenty feet wide, its bottom lost in black shadows. Larkwell studied the chasm carefully. "Might be just the rill we need for an airlock. If it's not too deep," he added. He picked up a boulder and dropped it over the edge, waiting expectantly. Crag chuckled. The construction man had forgotten that sound couldn't be transmitted through a vacuum. Larkwell caught the laugh in his earphones and smiled weakly. He said sheepishly, "Something else to learn." "We've plenty to learn." Crag looked both ways. To the right the chasm seemed to narrow and, although he wasn't sure, end.