Rogers ("Rodge") and Steve Jamnik, two young men returning from service at the end of WWII, stop by the office of Professor Burris to ask if he knows anything about a man named Frazier, and the new society Frazier is trying to build. Burris remembers that Frazier was a classmate of his in graduate school, one with radical ideas and a distaste for the establishment. He sends a letter to Frazier and immediately gets a reply inviting him to visit the community. Burris agrees to take time off from his academic duties to accompany Rogers and Steve on a visit to "Walden Two," Frazier's community. Rodge's girlfriend Barbara, Steve's girlfriend Mary, and Burris's colleague Castle also come.
Upon their arrival at Walden Two, they are greeted by Frazier. Over the course of their three-day visit, they are given a tour of Walden Two, a taste of what it is like to live and work there, and an earful of talk from Frazier about the planning that lies behind this utopian community. The population of Walden Two is about one thousand people, all of whom seem to be healthy and happy. They live in communal dwellings, eat in common dining spaces, raise their children in a communal nursery, and grow and build much of what they need. The standard workday lasts only four hours, or less; no one is paid wages--but nothing at Walden Two costs money.
How does Walden Two achieve this utopia? Through a science of behavior. Everything that is done at Walden Two is based on principles of behaviorism, the idea that human behavior can be controlled by manipulating contingencies of reward and, to a lesser extent, punishment. From an early age, members of Walden Two are conditioned to be productive and happy members of society. In line with its basis in science, Walden Two is an inherently experimental community. If there is evidence that a new social practice (e.g., not saying "thank you") will make people happier and healthier, it is immediately implemented and its consequences are carefully monitored.
Each of the visitors responds to the community differently. Castle finds it abhorrent; he spends the duration of the visit arguing with Frazier about the feasibility and desirability of a community like Walden Two. Burris, on the other hand, finds himself somewhere in the middle; he is skeptical that such a utopia could work, but he finds Frazier's arguments compelling, and he cannot discount the evidence of success in front of him. Steve and Mary are both convinced that this is the life for them; they decide to stay at Walden Two. Rodge, too, is convinced, but Barbara is not; he grudgingly leaves Walden Two with her at the end of their visit. Burris is torn, but decides to return to his academic life. However, at the train station he suddenly realizes that he would rather try life at Walden Two, for whatever it's worth, than go back to the university. He walks back to Walden Two and begins his new life there.
In the last chapter, an epilogue, he and Frazier discuss the writing and publishing of the preceding narrative as a way of spreading the word about Walden Two.