Ten-year-old Marvin is going outside, to the surface of the moon, for the first time ever—a stark contrast to his ancestors on earth, who went outside all the time. This, too, is the first time he sees stars. Unlike his human ancestors, he lives underground in sterile, controlled environment.

As he watches the earth hanging in the sky, he remembers all the differences between it and life on the moon that he has been taught about and seen on film. As he has learned, his ancestors walked on beaches, heard the sound of rain, and experienced snowfalls:

There in that shining crescent were all the wonders that he had never known—the hues of sunset skies, the moaning of the sea on pebbled shores, the patter of falling rain, the unhurried benison of snow. These and a thousand others should have been his rightful heritage, but he knew them only from the books and ancient records, and the thought filled him with the anguish of exile.

We also learn that Marvin has never walked by a river or heard the crash of thunder or experienced the many colors of earth. This is because a nuclear war made the earth uninhabitable due to radioactivity. It will be many generations—past the time the Marvin has died—before humans can safely return to their home planet, but Marvin will pass his knowledge of earth on to his own children. Meanwhile, he will live a much diminished life on the moon—knowing, however, that one day humans will return home.