Clarke's story has two main characters: Marvin, a ten-year-old boy, and his father.
Marvin is a sensitive boy who lives underground on the moon with other survivors of a nuclear holocaust that happened on earth. He is too young to have ever been on earth, so he has no memories of it. He is excited to be on the surface of the moon and reacts in a positive way to its beauties. Marvin is most excited, however, to see the earth hanging in the sky, yet he also feels the frustration of what has happened to it. He thinks:
Why could they not return? It seemed so peaceful beneath those lines of marching cloud. Then Marvin, his eyes no longer blinded by the glare, saw that the portion of the disk that should have been in darkness was gleaming faintly with an evil phosphorescence: and he remembered. He was looking upon the funeral pyre of a world— upon the radioactive aftermath of Armageddon.
Marvin is saddened. His father, too, regrets what has been done to the planet, which he remembers living on. He finds it of supreme importance to transmit to Marvin what it was like and the dream of humans returning to it hundreds of years in the future, when it is once again inhabitable. Marvin realizes that:
Yet one day—how far ahead?—his children's children would return to claim their heritage.
Marvin knows that he will transmit the same story to his children that his father told them. He is a character who represents hope for a future he will not see. He and his father are not cynical and despairing but full of optimism despite all that has happened.