The night after the ceremony, the serum induces a simulation and all the Dauntless become sleep-walking soldiers under orders to attack the Abnegation compound. The serum doesn't work on Tris or Tobias (Four) because they are Divergent. Tris and Tobias try to break away from the pack and escape as they arrive at the Abnegation compound, but Tris is shot and wounded. Tobias refuses to leave her behind and they are captured and brought before Jeanine, the Erudite leader who is the mastermind of the whole attack. She injects Four with an experimental serum that overrides his Divergent ability to control what he can see and hear. Jeanine directs Tobias back to the Dauntless control room to oversee the attack and sentences Tris to death. Tris wakes up sealed inside a real-life glass tank that fills up with water, but her mother breaks the tank and rescues her. Her mother reveals that she is also Divergent before she is killed helping Tris escape. Tris gets away but is forced to kill Will, who attacks her under the influence of the simulation.
She finds her father, Andrew, and Marcus in the safe house. They head to the Dauntless compound to find the source of the simulation and fight their way through to Dauntless headquarters. Tris' father sacrifices himself to clear the way for her to reach the control room. She confronts the mind-controlled Tobias, who attacks her. Tris realizes she can't bring herself to kill him, and surrenders. This causes Tobias to break through the special sight-and-sound-only simulation. Freed, Tobias helps Tris shut down the Erudite simulation and free the Dauntless from their mind control. They rejoin Caleb, Marcus and Peter, who helped Tris find the control room in exchange for his safety. The group boards a train to the Amity sector to find the rest of the Abnegation survivors