In a futuristic dystopian Chicago, the survivors of a mysterious great war live in what's left of the downtown behind a great wall keeping something unknown out, the climate is unexplainedly dry and mild, with the Lake dried up. The society is divided into Six factions: Abnegation (the selfless, pejoratively called stiffs), Amity (the peaceful), Candor (the honest), Dauntless (the brave), and Erudite (the intelligent), and those not faction members are simply called Factionless. Members join a faction based on their preference but are initially given a suggestion by an aptitude test. Beatrice Prior (Shailene Woodley) has grown up in Abnegation, the faction that runs the government, yet has always been fascinated by Dauntless. Her father, Andrew (Tony Goldwyn), serves on the ruling council along with the head of Abnegation, Marcus Eaton (Ray Stevenson).
Every year, 16-year-olds undergo a serum-based aptitude test that indicates the faction into which they would best fit and informs their choice at the Choosing Ceremony. Beatrice takes the test with a Dauntless woman named Tori (Maggie Q) as her proctor. Her test shows attributes of three factions (Abnegation, Erudite and Dauntless), meaning she is Divergent. Tori records her result as Abnegation and warns her to keep the true result a secret, telling her that since Divergents can think independently and the government therefore cannot control them, they are considered threats to the existing social order.
The next day at the Choosing Ceremony, Beatrice's brother Caleb (Ansel Elgort) chooses Erudite, while with hesitation, Beatrice chooses Dauntless. After the ceremony, Beatrice meets Christina (Zoë Kravitz) and Al (Christian Madsen), two Candors who chose Dauntless, and Will (Ben Lloyd-Hughes), an Erudite who also chose Dauntless. The Dauntless initiates are given tests such as jumping from a moving train and taking a leap of faith from a tall building into a large dark hole. During these tests, the initiates meet Eric (Jai Courtney), a brutal leader of Dauntless, and Four (Theo James), the transfer initiates' instructor. Beatrice volunteers first to jump off the building and leap into the hole, which has her branded as First Jumper. After the jump, when Four asks her name, Beatrice decides to shorten it to "Tris."
Tris initially struggles in Dauntless training, ranking 32nd out of 33 after the first evaluation, but slowly improves. After being forced to fight her enemy Peter (Miles Teller) and being hospitalized, Tris almost fails out of Dauntless, but redeems herself by playing a key role in winning a capture-the-flag game.
After the physical stage of Dauntless training, the initiates are put into simulations in order to face their fears. Tris' divergence allows her to excel at these tests, but Four warns her to conceal the reasons behind her success and to solve the challenges the way a true Dauntless would.
Tris visits her brother, Caleb, in Erudite, who tells her that Erudite is planning to overthrow Abnegation and become the ruling faction. On her return to Dauntless headquarters, Tris is attacked due to her success in training, with Peter, Al, and Drew attempting to throw her into a chasm, but Four slams Drew's head into a wall and fatally injures him and injures Peter and Al, saving Tris. The next day, Al pleads with Tris for her forgiveness but she refuses and calls him a coward. Later, she is shocked to learn Al has killed himself by jumping into the chasm.
In preparation for her final test, Four takes Tris into his own fear simulations, where she finds out that one of his fears is taking orders he doesn't want to do. She also finds out that his real name is Tobias, and he is the son of Abnegation leader and head of government, Marcus Eaton. After the simulation, Four and Tris realize their feelings for each other and share a romantic kiss. When the day of the test comes, Tris passes without revealing she is Divergent and is officially initiated into Dauntless. During the post-test celebration, the Dauntless are injected with a serum which is said to be administered as a tracking device, but which is revealed to be a mind control serum.
Controlling the heavily armed members of Dauntless through the serum, Erudite manipulates them into attacking Abnegation. Divergents are unaffected, so Tris and Four have to blend in and act as though they are affected by the serum. During a raid at Abnegation, Eric spots that Four is not under mind-control, and he and Tris both get captured. They are brought to the Erudite overseers, one of whom publicly identifies Four as Tobias Eaton. Four gets separated from Tris while she subsequently is about to be executed. Tris' mother Natalie (Ashley Judd) appears and rescues Tris. Her heroic act of bravery then reveals that she once was Dauntless. During the escape, Tris is forced to kill Will when, under the effects of the serum, he attacks her. Shortly after an attempt to cross an alleyway, Tris' mother is shot and killed.
Tris seeks her father for help to stop Erudite's plan. Tris, her father, brother, and Marcus sneak into the Dauntless headquarters. Seeing that Peter is not under the serum, Tris orders him to take them to Erudite's operations room. Her father sacrifices himself in a shootout. Tris goes in alone and finds Four, who is now under a more advanced form of mind-control that works even on Divergents. After a fight she manages to wake him from his stupor, knowing he cannot shoot her while looking at her face, for that is one of his fears. Tris and Four fight their way to the command center, where Erudite leader Jeanine (Kate Winslet) is about to start the protocols that will make Dauntless kill every Abnegation. Before Jeanine pushes the button, Tris intervenes by throwing a knife that stabs Jeanine's hand. Tris cannot make Jeanine abort the program nor kill her since she knows the code. Instead, she injects Jeanine with the serum and orders her to stop the program. Jeanine does as she is told and when everyone is released from mind-control, she is as well and attacks Tris. Tris knocks her out and escapes the Dauntless compound with Caleb, Peter, Four, and Marcus on the train, intending to ride to the end of the tracks.
