Insurgent begins a mere hour after Divergent ends. (If it's been longer than an hour for you, make sure to recap yourself with our Divergent guide. Veronica Roth is not going to help you in this one.) Tris has killed her friend Will, stopped a nasty simulation, and started a whole series of (unfortunate) events that will change the city forever.
But first, Tris and her friends need to hide. They're fugitives from what passes as the law around here. They find refuge in the Amity compound. Tris's first action, after her wounds are tended to, is to cut her hair, Lifetime Original Movie-style. With her new shorter haircut, Tris feels daring (or should we say Dauntless?) enough to track down her boyfriend Tobias's father, Marcus, and try to figure out exactly what he's up to. The answer: he's not telling.
While Tris is distracted by her boyfriend's dad (not in that way), Peter sneaks into her room and tries to steal the hard-drive with the simulation data. Hey, people still use hard drives in the future? Everything isn't in the cloud? Anyway, she catches him and beats the snot out of him. As punishment for violating Amity's rules of peace, she's injected with super happy juice, a.k.a. peace serum.
As soon as it wears off, Erudite arrives with a band of Dauntless traitors. They're looking for Tris and company, and a huge fight breaks out. Tris and her buds escape the Amity compound and find themselves on a midnight train to Geo… —er, to factionless-ville. At the factionless safe house, Tris finds out that Tobias's mom, Evelyn, is still alive and has a plan of her own to take over the city.
Confused by all these different motives, Tris goes to the Candor headquarters to find out what's going on. The tables are turned when she's injected with truth serum and forced to confess everything, like the fact that she killed Will. This shocks her friend Christina, who loved Will and had no idea Tris shot him. Hello, tension.
After the interrogation, Tris considers jumping out the window and ending it all but decides not to. She reunites with her Dauntless friends Uriah, Marlene, and Lynn, who are living at the Candor compound. The reunion is short-lived because a bunch of Dauntless traitors, headed by Eric the Dauntless leader, attack the compound. Tris gets caught by Eric but stabs him in the gut.
Once the smoke clears, Jack Kang, head of the Candor, sets up a peace treaty meeting with Jeanine. Tris and her friends spy on them. Jack ends up meeting with Max, one of Jeanine's henchmen, and Lynn shoots Max. Um, good job? Things get real pretty quickly (again). Lynn's sister is shot, and Peter ends up turning traitor (no surprise there). He helps Jeanine escape.
Back at the compound, Tori and Zeke arrive and tell everyone that they weren't actually traitors, just spies. Tori calls a meeting in which three new Dauntless leaders are elected: Tori, Tobias, and Harrison. (No, we have no clue who Harrison is, either.) They kill Eric (Eric the Red, meet Eric the Dead) so that Jack Kang cannot accede to Jeanine's demands, and then they reclaim the old Dauntless headquarters.
One night, Tobias has a meeting with Evelyn, and he brings Tris along to analyze the situation. Her analysis: Bad News, Dead Ahead. But Tobias ignores her, which causes a huge fight. When Jeanine later activates a simulation that causes Marlene to jump off the building and kill herself (the city's suicide method of choice, it seems), Tris decides to turn herself in to Jeanine. If Jeanine wants the Divergent, the Divergent is what she's going to get.
Jeanine runs a few tests on Tris, finding out that her brain is different from non-Divergent brains, then decides to execute her. With the help of Peter (yes, that Peter—who won't he betray?), Tobias saves Tris from execution, and they flee. They go to Tobias's old house in the Abnegation sector. When Evelyn reveals her plan to eradicate the Erudite, everyone is all gung-ho about it… except Tris. Tris is like, "No revolution tonight, honey; I have a headache"—meaning that she pretends to be too scared to go. She decides to assist Marcus instead, who wants to get the top-secret data from Jeanine.
With the help of Johanna Reyes, the Amity representative, and some sympathetic Erudite—like Cara, Will's sister—Tris and Marcus reach the top of the Erudite building where Tris was being studied. Unfortunately, they're too late. Tori stabs Jeanine, despite Tris's protests, and the Dauntless/Factionless assault on Erudite succeeds.
They all go back and celebrate, and Evelyn reveals her true plan: to eliminate all the factions. Before this sinks in, Tobias shows up with Marcus and Johanna. They've got a video they recovered after hacking into the computer system. (We guess the cloud does exist after all, rendering this whole storm-the-castle operation totally pointless... but let's not quibble.) In the video, a woman who calls herself Edith Prior says that the outside world is in danger, and everyone in the city was placed there as some sort of experiment to save humanity. The Divergent ones are the people who will save us all. And… curtain.
Holy cliffhanger, Batman!