The moon is a boring, dangerous, unpleasant place to live, but research must be done and, eventually, a colony is to be established. So scientists are sent up for 18-month shifts to work there, and they are very eager to return when their time is up.

Chapman has been on the moon for three years, and he's no scientist; he was the pilot who brought the first group, and he stayed on when they returned, to help ease the transition for the relief group, and to help keep them from making deadly mistakes, as one of the first group--Dixon--had done.

Chapman has a wife waiting for him back on Earth, and he can't be off the moon soon enough--but they want him to stay, again. They're building a colony. They need his experience. He's having none of it. Another man will take his place.

However, he receives a letter from his fiancee, Ginny, and opens it just before leaving. She's breaking it off with him; three years was too long to wait. Crushed, Chapman tells them he'll stay on the moon. He has nothing to return to.

Ginny, it turns out, didn't want to break it off with him. But she--Ginny Dixon, whose brother died on the moon--knows how important it is for a man like Chapman to be there, to prevent further tragedy. So she was convinced to write the letter, to force him to stay.

We see, in the far future, that the colony is successful, and that Ginny has joined Chapman on the moon, and that now their son is considering whether he can leave his girl for years on a mission to a distant world.