"Insurgent” by Veronica Roth is the second book in the Divergent trilogy. The sequel begins with Tris, Caleb, Tobias (aka Four), Peter, and Marcus on a train headed toward Amity where they hope to take refuge, at least for one night. If anyone will offer shelter, it will be Amity. Still struggling with the death of Will, at her own hands, Tris cuts her hair signifying her final transition to a Dauntless identity.

Arriving at the Amity compound, the group meets Johanna Reyes, a beautiful woman marred by a large scar on her face. Johanna is the spokeswoman for the compound. The group fears that they might be turned away and captured by Dauntless and Erudite gunmen. However, Johanna tells them that Amity has decided to offer sanctuary to each of the factions and that the group will be welcome to stay for the night. A vote will be taken by Amity to determine whether they will be allowed to stay longer.

The next morning, Tris wakes and finds she is wearing the same clothes as the previous night. She spots the corner of the hard drive peeking out from its hiding place. The drive stores the simulation data that controls the Dauntless and the records of the Erudite faction's activities. Tris would like to destroy it. Instead, she keeps it hidden because it stores the only information about her parents' deaths. She and Tobias have determined that they must locate Marcus, Tobias's father, who knows more than he's telling.

At Amity, Tris is reunited with old friends such as Susan, who is a very caring woman. Susan tells most of what she knows. Yet, Tris feels like Susan is holding something back. The next night Peter tries to steal the hard disk from Tris, but Tris retaliates and nearly kills Peter in the ensuing fight. This is forbidden within Amity's safe haven and Tris is subjected to a dose of 'peace serum' which renders her unable to think clearly. The Amity council determine that the group have outstayed their welcome and must leave the next day.

As they are readying themselves to leave members from the Erudite city arrive with a group of Dauntless who've agreed to work with them to hunt down Tris and her group of divergent thinkers. A large fight ensues and Tris's group manages to escape by jumping on a train headed to the places where only the factionless live. The factionless are those who were never assigned a group to live with. Living displaced and homeless it was assumed that there weren't that many of them, and that, for the most part, they were a fringe element. However, when they arrive and are taken to factionless safe houses, they not only learn that the factionless number is in the thousands, but that their leader is none other than Tobias's mother, Evelyn. Evelyn, whom Tobias was told was dead all these years, has a plan to take back the city and to do away with the faction system.

Tris decides that she can trust some of those living in the Candor community (mainly because of her friendship with Christina a former Candor member). But, once she is there she is betrayed and is considered a rebel. They subject her to a truth serum in a live forum and her memories and knowledge are laid bare for all to see. When she confesses that she killed Will, her friend Christina who was in love with Will, knows the truth. Though Christina understands that Will wasn't acting of his own accord, she blames Tris for not disabling him as opposed to killing him. Tris feels the same way and blames herself for her actions. Despondent, Tris considers ending her troubles by jumping out of a window to her death.

It is her relationship with Tobias (Four) that makes her back away from the window. He convinces her that together they can right the ship and that it will take both of them working with his mother and the factionless to make it work. They are still determined to locate Marcus and force him to tell them the truth about the faction system and how they all came to be where they find themselves. She reunites with Uriah, Marlene, and Lynn who have been living with the Candor for a short while. Before they can formulate a plan the compound is stormed by the renegade Dauntless soldiers lead by Eric. Eric manages to capture Tris but she gets in a good lick by stabbing him with her knife before she is knocked unconscious.

At the center of everything is the Erudite leader, Jeanine, whom Tris's brother, Caleb has aligned himself with. The leader of the Candor sect sets up a meeting to mediate a peace plan between the factions. This includes Jeanine, Kang, and Eric. Tris and Tobias spy on them and when Jack meets with Max (Jeanine's right hand man) Lynn kills him. Lynn's sister is shot in the process and Peter betrays them all by siding with Jeanine and getting her out of the building unharmed.

Tori and Zeke return to the new Dauntless compound and are almost killed. They convince everyone that they were just acting as spies and they give them valuable intel on Jeanine's plans. They find, capture, and kill Eric so that no more Dauntless soldiers will have to be experimented on or used by Erudites. They can now reclaim their old compound, which they do. Tobias and Tris's relationship grows deeper.

Meanwhile, Tobias is trying to wrap his mind around the fact that his mother is still alive. He introduces Tris to her with the hope that Tris will be able to discern what Evelyn's ultimate agenda might be. Tris's assessment is less than flattering and it upsets Tobias, who argues with her assessment. They argue and become estranged.

Jeanine activates a sim drug in one of their group members, Marlene, who jumps to her death. An ultimatum is issued: bring Tris to Erudite headquarters or more Dauntless will be activated to commit suicide. Tris decides to give Jeanine what she wants. When Jeanine has Tris she runs massive tests, many of them painful, on Tris and determines that Tris's brain chemistry and structure is different from most others' brains. This has allowed her to be a divergent thinker. The conclusion she comes to is that Tris must be executed. Peter assists Jeanine in the experiments on Tris, as does Caleb, Tris's brother.

In a daring rescue, facilitated by Caleb and Tobias, Tris is rescued and taken to the factionless compound. Here, she finds that she must make a choice between following either Tobias's mother's plan to storm the Erudite headquarters, or assist Marcus who wants to retrieve the data from Jeanine that explains the entire Divergent experiment. Faking illness and injury, Tris opts to help Marcus, even though she knows that eventually Tobias will see it as a betrayal (he and his father dislike one another).

Along with Marcus, Tris, Tori, and Cara (Will's sister) manage to make it into the Erudite headquarters and upload the data to a drive. They had hoped to take Jeanine alive to interrogate but Tori stabs Jeanine because she had previously killed her brother. Simultaneously the Factionless/Dauntless assault on the headquarters commences and the building is overrun.

While celebrating back at their factionless headquarters, Evelyn unveils her ultimate plan: eliminate the faction system once and for all. Marcus, Johanna and Tris show up with the data that they've retrieved. A woman is on the tape, a woman calling herself Edith Prior talks about a grand experiment to save humanity. The woman on the tape looks like a much younger version of Tris's mother. She explains that mankind was destroying itself in many pointless and devastating wars. They were sectioned off to see how mankind might develop, knowing that one day evolution would help them save themselves by producing divergent thinkers. The entire experiment was to produce divergent thinkers. It is revealed that Jeanine knew this all along as she was also one of the experiment's founders, but loved her position and power too much to let the experiment succeed.

Her words on the screen shock everyone, especially Tris and Tobias, who've reconciled. They realize that the divergent, like themselves, were destined to play a greater role in the salvation of mankind.