A nuclear war has changed the world. An amendment to the U.S. Constitution prohibits cities of more than one thousand people or two hundred buildings to the square mile, technology has been condemned, and religious fundamentalism holds sway. First cousins Len and Esau Colter dream of a place called Bartorstown, where men work to revive the cities and their precatastrophe technology. To speak of that place is dangerous; they see a man who did so killed.
Len and Esau acquire a radio, steal three books from a local teacher, get caught, are sentenced to a public birching, and decide to run away. They eventually reach Refuge, a city on the Ohio River, and go to work for a local businessman, Mike Dulinsky, whose expansion efforts violate federal laws and raise fears of a future holocaust. Dulinsky erects a new warehouse, violating the building restriction. When he tries to explain at a public rally why the town should grow, he is murdered by angry farmers, and Len nearly is hung for helping him. A trader named Hostetter appears and helps Len, Esau, and Amity Taylor, who is in love with Esau, to escape on a barge. He will take them to Bartorstown but warns them that it may not be what they have imagined.
After a long journey, they reach the mythical place, formerly a secret government project, buried deep in the Rocky Mountains. They are told that if they attempt to leave, they will be shot. Len is attracted to Joan Wepplo. Because Amity is pregnant, she and Esau are married.
Bartorstown houses an atomic reactor. The secret proj-ect was to create a force field to prevent an atomic reaction from occurring, but that has not yet been accomplished. Len falls in love with Joan, but she wants to leave Bartorstown. Pressed by Joan, fearful that the religious fundamentalists may be right, and depressed because the town’s most recent solution to the problem has failed, Len decides to leave. He and Joan marry, giving them a long holiday. They escape and evade capture for several weeks. During their trip, Joan becomes disillusioned with life outside, and Len realizes that he cannot return to his childhood. Hostetter finds them later and gives Len a chance to denounce him, but Len does not. He and Joan return to Bartorstown.