The novel is full of many twists.
Background: Nick and Amy Dunne are husband and wife. They have been married for five years. They are starting to grow apart, in part because Nick is having an affair. On the day of their anniversary, Amy disappears and a bloody crime scene is left behind.
Nick is the number one suspect in the case because he does not act like a grieving husband and because of clues Amy left him before she disappeared as an anniversary scavenger hunt. Huge credit card charges come up on Nick's cards, and a large number of electronics are found in the couple's shed. This makes the detectives think that Nick was having money troubles and that he may have killed his wife.
Meanwhile, Amy is alive and well, and on the run. She intends to kill herself and position her body so that it can be found and Nick could go to jail for murder. She is using this plot as revenge.
She eventually decides not to kill herself, and contacts an ex-boyfriend, who invites her to stay at a secluded house. Amy does not want his sexual advances and kills him. She returns home, covered in blood, saying that her ex had kidnapped her but that she had escaped.
Nick does not believe Amy and confronts her. She admits that she set him up. However, in the eyes of the media, they are a happy, reunited couple.