Harry Bittering and his family move from Earth to Mars to take part in a new colony. When they arrive via rocketship, however, Harry quickly feels that something is wrong with the Martian environment, and that it is already working gradual and insidious changes upon his family. Although they continue into town and set up a comfortable lifestyle in the new settlement, Harry cannot shake the feeling that something is wrong. His children, too, have a sense of unease concerning the old, long-abandoned Martian settlements and the planet as a whole.
After a few weeks have passed, the news comes that Earth has become embroiled in nuclear war and that no more rockets will arrive from the planet, effectively stranding the new settlers on Mars. While Harry is upset at this news, the others quickly accept the reality of their situation and settle more deeply into their lives on Mars. A few days later, Harry notices changes in the plants and animals that they have brought from Earth, which have shifted in color, scent, and taste. Even more upsetting, the physical characteristics of the settlers are changing: they are becoming taller, with dark skin and golden eyes more suited to the Martian environment.
While Harry is horrified by this, the other settlers are, again, less bothered. Harry insists on beginning work on a rocket to return to Earth, but no one else volunteers to help him in his futile endeavor. Eventually, Cora persuades him to go for a picnic and a swim, and he gradually begins viewing the changes he and his family have undergone with more ambivalence than fear. They explore Martian villas in the mountains and reflect upon how pleasant and well suited the structures are to the environment. When he and his family eventually return to town, Harry loses steam on his rocket project, viewing it with less enthusiasm than before.
Harry sees other settlers packing up and learns that they are moving up to the Martian villas for the summer. His family persuades him that they should move as well, and they leave most of their possessions behind them as they do so. Harry’s family, like the rest of the settlers, have gradually forgotten everything about their origins to the point that they no longer remember that they are from Earth at all. Instead, they happily inhabit the mountain villas and do not return to the abandoned settlement. Harry and Cora reflect on the “ridiculous” houses of the “ugly” Earth people, whom they’re “glad” have gone.
Five years later, men from Earth arrive announcing that they’ve won the war. They’re startled to realize that the settlement has been abandoned, and mistake the old settlers, who have completely forgotten their origins, for native Martians. As one of the men, a captain, begin plans to reconstruct and expand the settlement with new people from Earth, his Lieutenant seems not to listen, instead gazing into the misty Martian hills.