n a post-apocalyptic Chicago, survivors were divided 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 intellectual. Each year, all sixteen-year-olds take an aptitude test that describes the faction for which they are best suited. After receiving the results, test takers choose a faction, no matter what their results were. 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 she belongs in Abnegation, because she doesn't see herself as naturally selfless. Her aptitude test results are inconclusive and indicate aptitude for three factions – Abnegation, Erudite, and Dauntless. The test proctor warns her never to tell anyone that her results were inconclusive because that makes her a "Divergent." Beatrice agonizes over Choosing Day, unsure about staying in Abnegation with her parents or moving to a different faction. On Choosing Day Beatrice decides to leave Abnegation and join Dauntless. Her brother Caleb chooses Erudite.
The Dauntless instructor, Four, explains that not all Dauntless initiates will be allowed to enter the faction. The initiates will have to go through a series of training and evaluation. Unusual to this faction, only the top ten will stay, while the rest will be dismissed and become factionless; by contrast, the other factions allow everyone who completes initiation to enter. During her initiation, Beatrice renames herself Tris and befriends transfer initiates Christina, Al, and Will, but comes into conflict with fellow initiates Peter, Drew, and Molly. She also befriends Dauntless-born initiates Uriah, Lynn, and Marlene.
The Willis (or Sears) Tower, one of several landmarks Roth describes within post-apocalyptic Chicago, the novel's setting.
Initiation into Dauntless is composed of three stages. The first involves learning how to handle guns and knives and hand-to-hand combat with other initiates. Tris lacks the physical strength of most of her fellow initiates, but finishes in sixth place by beating the higher-ranked Molly. When the rankings are announced, a jealous Peter, who finished second, stabs first-place finisher Edward in the eye with a butter knife during the night.
The parents have a visiting day and Tris realizes her mother's original faction was Dauntless.
Erudite stirs dissent against Abnegation leadership in the city's government and accuses Marcus, the Abnegation leader, of abusing his son. The fact that Marcus's son joined Dauntless two years before and that Tris' parents' children also switched factions instead of remaining in Abnegation, adds to the rumors. Abnegation is also alleged to be hoarding supplies.
The initiates enter Stage 2 of their training, which involves simulations similar to the aptitude tests. Initiates are forced to face scenarios based upon their deepest fears. The simulations act in a hypnotic fashion and initiates forget their situation isn't real. Tris' Divergent abilities enable her to remember that she's under a simulation. She uses this advantage and wins top rank in the class. Peter, Drew, and Al attack Tris in revenge with a threatened sexual assault and attempts to kill her by throwing her into the chasm at Dauntless headquarters. Four intervenes and stops it. Later, Al begs for Tris's forgiveness, but she rebuffs him. He later commits suicide by jumping into the chasm where he tried to kill Tris.
The final stage of Dauntless initiation gathers all their fears in a single simulation landscape. All the initiates, including the Divergents, are aware they are under a simulation and must use the skills they've learned in the previous stages to overcome each obstacle. Tris's relationship with Four continues to grow as she prepares for this stage of testing, and he lets her into his own fear landscape. Four has four fears in his landscape, hence his nickname, which is a low number that's rarely heard of. She also learns he is really Marcus's son Tobias, the child of the Abnegation leader the Erudites accused of child abuse. Four shares information he discovered about Erudite's plans to use Dauntless to stage an attack on Abnegation with Tris.
Tris successfully overcomes seven fears in her fear landscape. After her test she and the other Dauntless members are injected with a new "tracking" serum that supposedly activates if someone goes missing.
Before the official initiation ceremony, Four invites Tris back to his private apartment, and Tris expresses her feelings for him. The ceremony begins with the post of final rankings and Tris is ranked first. In the midst of celebrating she suddenly realizes Erudite will use the "tracking" serum to force Dauntless members to carry out their invasion of Abnegation.