The book picks up with America and Maxon on a date. The caste is under attack from rebels so they go inside the palace. Maxon takes America to a room full of illegal books and he teaches her about the special holiday, Halloween. Maxon wants to make America happy so he decided to hold her a Halloween party.
The morning of the ball, America learns that Marlee was caught having an affair with a palace guard, Carter, and as punishment, both will be lashed 15 times and stripped down to Caste Eight. America cannot witness the action against her friend so she tries to stop it but is instead taken to her room. Maxon visits her and she lashes out at him saying it is his fault for letting the punishment happen. Maxon helps to get Marlee and Carter’s castes back up to Six and allows them to continue working in the palace.
Maxon lets America borrow a book from the illegal library and she learns of Gregory Illéa's diaries, which details how he changed Illéa from a democratic government into a monarchy so that he could become king.
Rebels attack the palace the next day and America climbs a tree to hide from sight. She witnesses a girl and boy taking books from the palace. The girl sees America but only bows at her. Aspen finds America and takes her back. America realizes that the rebels want to find Gregory Illéa's diary.
At the same time, America’s jealousy grows due to Maxon spending time with the other Elites. She becomes jealous when she sees him with Celeste and comes to the conclusion that Aspen is the one for her.
As part of the Selection, the girls have to carry out a debate on live television. America’s debate is to eliminate the Caste system and she draws on Gregory Illéa's initial formation of the system. The King, who is angry and confused as to how she knows so much about it, cuts off her debate. Maxon defends her and tells his father that he brought America to the room with illegal books.
The rebels attack again, and America and Maxon hide in a room where America learns that his father, due to America’s actions, has whipped Maxon. She also notices older scars on his back. America admits her jealousy of the other girls and Maxon admits that he was going to propose to America the night of the ball.
America believes that Maxon will eliminate her so she leaves the palace. However, Maxon stops her and asks her to remain. The King confronts America and threatens America to not make him her enemy.