Living in the cactus was more satisfactory than living outside. Shaan made it his headquarters. He slept in it at night, amid the furry animals, which accepted his presence without question, merely avoiding any close approach. By day, he crawled out in search of the dome. He did it systematically, going in a different direction each day. He tried sixteen directions without success. A day just wasn't long enough. The second two-day trip he made, going out one day, sleeping out and returning the second day, he saw the sun flash off a faraway plastic dome at midafternoon. * * * * * Shaan pushed his face through the leaves and stared across a hundred-foot cleared space at the dome. The canal sage was very efficient. When the space had been cleared for the dome, the sage foliage had grown down to the ground level around the bare circle to prevent the life-giving oxygen under it from dissipating. The transparent hemisphere glistened dully in the sunlight. It covered about an acre of ground. Near one side was the small home of a canal settler. Under the protective dome terrestrial vegetables grew and terrestrial animals lived. Long ago Shaan had jettisoned his oxygen cylinders to save weight, but they would have done him no good had he kept them. His marshelmet, however, would hold enough air for him to cross the cleared area to the dome. He pulled it on, under the leaves. Then he remembered something and took it off again. He smeared dirt over the brand on his forehead, hoping he was concealing it. He put the helmet back on. Getting to his feet, he ran across the clearing and through the open outer door of the airlock. He shut it behind him and, waiting a few minutes, took off the helmet. There was air in the airlock. He had done this without fear or reflection. On a planet like Mars, only a thin line of oxygen stood between life and death. The outer door to every airlock on every dome stood open unless the inner door was opened, and oxygen automatically filled the airlock when the outer door was closed. It was a custom which could save lives. The inner airlock door was a different proposition. No one liked to be caught unawares by visitors. It was locked. Shaan knew the closing of the outer airlock door had set off an alarm inside the dome. He waited. He could see the house and the gardens, a little distorted, through the transparent plastic of the inner door. After a few moments, a figure emerged from the house and approached the airlock. When the figure got closer, it became a young woman in the shorts and blouse customarily worn inside the domes. She held a heat-gun in her hand. "Who is it?" she asked through the communicator. "I'm Robbo Shaan," he answered. "I'm a government mail pilot. My plane went down on the desert." "Why didn't you wait for rescue?" "Radio went out before I crashed. Helmet radio, too. I'll have to call for help from here." "You can wait in the airlock. I'll radio Mars City."