A young man identified only by a number narrates life inside a totalitarian society that forbids individuality, personal names, and independent thought. Assigned a prescribed vocational role, he secretly pursues scientific inquiry, discovers a hidden tunnel and an abandoned technological artifact, and forms a forbidden bond with a woman who is also numbered. His experiments lead him to rediscover the concept of the individual and the word I, prompting a rejection of imposed doctrine, an escape from the city, and an attempt to start anew on principles of personal freedom and reason. Themes include autonomy, the pursuit of knowledge, and the moral claim of the individual.