Divergent is the first installment in a science-fiction trilogy, and is narrated by a 16 year old girl called Beatrice Prior. The setting is a futuristic city which, though not specified in the novel, closely resembles Chicago.  The city has been split into five factions: Abnegation, Dauntless, Erudite, Amity, and Candor. The idea behind this split is that human conflict has not been caused by political ideology, race, religion, or nationalism but by differences between personality types. This prompted people to form factions in an attempt to focus on more positive values. For example, Candor sees dishonesty as the source of conflict and therefore prioritizes telling the truth.

Beatrice has spent her whole life living with her parents and brother in Abnegation, but she has never felt as though she fits in. She recognizes that this faction must look ideal from the outside, as it offers a peaceful existence and everyone helps one another. However, she finds its uniformity confining and does not believe that she is sufficiently selfless to belong in this faction. 

At the start of the novel, Beatrice, like other people her age, is due to undergo an aptitude test which is supposed to indicate the faction to which she is best suited. This will be followed by a choosing ceremony, in which she will make the ultimate choice: to stay with her family in Abnegation or transfer to a new faction in which she will spend the rest of her life. This is not a choice to be made lightly, as the faction to which a person belongs is seen to be a critical part of who they are and is deemed more important than family. To be factionless is to live a menial, impoverished existence with no sense of belonging, and this is regarded as a fate worse than death.

Though Beatrice completes her aptitude test, her results are puzzling: the test is intended to rule out one faction after another in a linear manner, yet Beatrice shows an aptitude for Abnegation, Dauntless, and Erudite. This is not merely an inconclusive result though; it also marks Beatrice out as Divergent. Beatrice does not understand what this means at first, but she understands that it is seen as dangerous and that she should not reveal her status to anyone.

During the choosing ceremony, Beatrice witnesses her brother—whom she had thought to be a perfect member of Abnegation—transfer to Erudite, and she is shocked. This makes her all the more conscious that she needs to transfer out of Abnegation, though she has no inclination to join Erudite. As is specified near the beginning of the novel, Erudite have been publishing damning reports about Abnegation and there is no love lost between these two factions. One of the root causes is that, though representatives from other factions can have a say in meetings, Abnegation members alone form the city’s governing council. This is because members of this faction are seen to possess the requisite selflessness, leadership skills, and moral fortitude necessary to make important political decisions. However, Erudite resents this monopoly and does not believe that the values of Abnegation adequately represent other factions.

With Erudite out of the question, Beatrice pledges allegiance to the faction to Dauntless, the faction to which she is most drawn. This is a faction that emphasizes strength and courage, and Beatrice has been fascinated by the sight of Dauntless students (who wear black and have multiple tattoos and piercings) leaping from the passing train to attend school. Still, she feels bad about leaving her family, and her father (who had assumed that both of his children would stay in their native faction) looks at her with an accusatory glare. Her mother, however, has already said that she will love her no matter what, and she smiles at Beatrice as she leaves.

Dauntless initiates are expected to hit the ground running, and Beatrice immediately finds herself engaged in nerve-wracking tasks such as jumping from trains and tall buildings. The training process begins with physical tasks such as fighting and target practice, before moving on to facing one’s fears in simulations much like the aptitude test. Beatrice quickly makes friends with some of the other initiates such as Will and Christina, though the faction also includes bullies such as Peter and his sidekicks Molly and Drew.  In addition, Beatrice renames herself Tris to signify the new life that she has embarked upon in Dauntless.  

There are two training instructors: Eric and a young man who goes by the nickname “Four.” Eric is ruthless and brutal, whereas Four is more reserved and intelligent. Tris finds herself attracted to Four, and the feeling proves to be mutual. Four’s true identity is finally revealed when he allows Tris to experience his fear landscape: a simulation that all Dauntless members must go through and that requires facing one’s worst fears. From his fear landscape, Tris learns that Four is in fact Tobias Eaton, who is the son of one of the high-ranking officials in Abnegation. Erudite have been reporting that Tobias left Abnegation because of his father’s cruelty, and this particular claim proves to be correct.

Tobias informs Tris that Dauntless did not used to be so brutal and competitive but, six years ago the leaders changed and instigated a new regime. Eric is an ideal match for Dauntless in its present guise, but Tobias has a different outlook. He believes that selflessness and bravery can be the same thing; moreover, he does not believe in splitting up personality traits into factions, or that the values of one faction are better than those of another.  Indeed, the faults of the faction system reach crisis point when Tobias and Tris realize that Erudite are planning war against Abnegation. Furthermore, Erudite have recruited Dauntless to help them, promising that they will be given a spot in the new government in exchange for their help.

Tris’s ranking has climbed higher and higher throughout the initiation period, and, once she has faced her own fear landscape, she finishes as the top-ranked initiate. However, the celebration period is short lived, as Tris realizes that the serum that Eric has administered to all members of Dauntless (supposedly to track them should they go outside the compound unattended) is intended to create an army of brainwashed soldiers. Sure enough, the Dauntless follow orders to file into the city and start killing members of the Abnegation council. It is also at this juncture that Tris realizes why Divergents are seen as dangerous: they cannot be controlled. This is shown by Tris’s—and Tobias’s—immunity to the serum.

Tris and Tobias are captured by Erudite guards but Tris is rescued by her mother, who is also Divergent (she had originally transferred from Dauntless to the safer faction of Abnegation, to minimize the danger associated with her true status). Tris’s mother sacrifices herself so that Tris can run away and join the other refugees from Abnegation; including her father and brother. Tobias, meanwhile, has been administered a new serum developed by Erudite that can alter what he sees and hears. So, while Divergents’ minds cannot be controlled, Erudite have found a way of manipulating them indirectly. This means that Tobias now sees Tris as an enemy.

Tris and the other escapees embark on a final mission to enter the Dauntless compound, with Tris and her father making their way to the control room. This is an extremely dangerous mission, and Tris’s father loses his life while fighting the guards. However, Tris manages to make her way to the control room, where she finds Tobias. He is poised to shoot her at first, but he manages to overcome the simulation and shut down the computer program that is controlling the members of Dauntless.

The city is now in chaos, and Tris and the other survivors make their way to the refuge of Amity. As Tris reflects on her experiences, she realizes that Tobias was right: self-sacrifice can be an act of bravery (as demonstrated by her parents), and she herself is not as selfish as she imagined. As for the future, Tris has no home or sense of certainty, but she knows that Dauntless and Erudite are bound to come looking for her and her fellow escapees.  Still, above all else, Tris has shown herself to be a fighter.