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."

"I'm hungry," he said, "and thirsty."

That was an appeal that could not be ignored.

"I'll let you in," she said after a moment's hesitation. "But I have a gun."

"I don't," he answered, spreading his hands and turning so she could see all around his belt.

The inner airlock door opened, and Shaan entered the dome. The smell of the air brought memories of his boyhood on Earth.

The girl stood away from him, holding the heat-gun on him steadily. She had brown eyes and red-gold hair that tumbled to her shoulders. Shaan judged her to be about 

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