The novel is set in a post-apocalyptic Chicago in which survivors divide into five factions based on their dispositions: Abnegation, for the selfless; Amity, for the peaceful; Candor, for the honest; Dauntless, for the brave; and Erudite, for the intelligent. Each year, all sixteen-year-olds take an aptitude test that describes the faction for which they are best suited. After receiving the results, they can decide whether to remain with their family's faction or transfer to a new faction. Those who do not complete initiation into their new faction become "Factionless", and are forced to live in poverty on the streets of the city.
Sixteen-year-old Beatrice Prior is born into an Abnegation family. She doesn't feel like she belongs in Abnegation, because she doesn't see herself as naturally selfless. Her aptitude test also supports this, inconclusively indicating aptitude for three factions: Abnegation, Erudite, and Dauntless. The tester warns her to never share this fact, as it makes her a Divergent. Before the Choosing Day, she agonizes over whether to stay in Abnegation to satisfy her parents, or whether she should change to another faction.