Two weeks after Amy's disappearance, Nick counts the hours until his arrest. The intense media coverage continues, exacerbated by the revelation of the contents of the shed and the existence of Amy's diary. Nick can only hope that his plan to lure Amy back to him will work. Although Nick publicly continues to tell the world how much he loves Amy, and how desperate he is for her return, he secretly harbors fantasies of murdering her as revenge. About a month after Amy's disappearance, the detectives recover the wooden handle of the Punch and Judy puppet from the river near Nick's home. The police test the handle and find traces of Amy's blood on it, confirming their belief that the handle was used as a murder weapon. Based on this evidence, the police declare the murder a homicide, and charge Nick with Amy's murder.
More time passes while Amy tries to figure out how she can escape from Desi's lake house. Under the guise of protecting her, Desi has made it impossible for her to leave the house. Desi also strictly controls how much she eats and what she wears, and while he waits patiently, Desi also makes it clear that he wants to have sex with Amy. Amy is repulsed by this idea. However, Desi's desire for Amy becomes a tool she can use as she develops her escape plan. Just like when she faked her disappearance, Amy carefully prepares. Forty days after she disappeared, Amy dresses in an outfit that she knows Desi will find attractive. She behaves seductively, and the two have sex. Afterwards, Amy brings Desi a martini into which she has dissolved a sleeping pill, causing him to pass out.
By mid-August, more than a month after Amy's disappearance, Nick awaits trial. He has been cleared to await trial outside of jail, so he still lives in his own home. Tanner is desperately trying to locate Amy but so far has not been successful, and Nick knows there is a good chance he will go to prison. One day, forty days after Amy's disappearance, the doorbell rings, and when Nick answers it, Amy is at the door. She is disheveled and bloody, and has pieces of rope tied around her wrists.
The first reaction Nick feels when Amy returns is rage. However, there are reporters everywhere, so Nicks acts as if he is overjoyed to see her. When Nick and Amy are alone inside the house, he questions her and Amy tells him that she was kidnapped by Desi and held hostage. Amy has only now been able to escape. Nick does not believe this story, and tells her that he knows she was framing him. At the same time, as Amy protests her innocence, Nick finds himself wanting to believe her. Before Nick and Amy can talk any more, the police arrive at the house.
As the police examine and question her, the details of how Amy escaped from Desi are revealed. After Desi passed out from the sleeping pills, she killed him with a knife, and then staged the scene to look like self-defense. Amy then left the house and drove to Carthage, making it look as though she was fleeing. Because Amy has Desi's semen inside of her, and because she has self-inflicted injuries consistent with rape and abuse, her story of being held captive and raped repeatedly is believable to the police. At the same time, as Amy is questioned, some inconsistencies appear, which makes the police suspicious. In order to protect herself, Amy accuses the police of mishandling the case. Amy points out that while the detectives were focusing on Nick, she was suffering, and that she only escaped due to her own ingenuity.
Nick goes to the police station to pick up Amy, where he finds everyone celebrating her return. Amy's parents apologize for not trusting him. Jacqueline Collings, Desi's mother, has arrived, and she is convinced that Amy has lied and deliberately murdered Desi. However, no one is interested in Jacqueline's story. When Amy and Nick are finally alone together, back at their house, Nick demands that she tell him the whole truth. Before Amy will tell the story, she insists that they get into the shower together, so that she can be certain Nick is not wearing a wire, and rely on the sound of the shower to cover up their conversation in case the house is bugged.
Nick is horrified and disgusted when he finally confronts the reality of Amy's full deception. Amy can tell that Nick might be considering telling someone the truth, so she unveils her remaining tool for blackmail. At the time when Amy described symptoms of poisoning in the diary, she actually did ingest antifreeze. When Amy vomited as a result of the poisoning, she saved and froze some of the vomit. If Nick doesn't support her plan, Amy can use the vomit to suggest that Nick poisoned her, and he could go on trial for attempted murder.
As soon as Amy goes to bed, Nick calls Tanner and tells him about Amy's confession. Tanner points out that without any proof, and with the significant evidence against Nick, the best thing to do is for Nick to play along with Amy's lies for the time being. Desperate and frustrated, Nick confronts Amy and suggests they get a divorce. Amy taunts Nick, pointing out that he needs her. Enraged, Nick starts to strangle her. Then he realizes that he cannot imagine life without Amy, and that he feels a need to outwit her. Nick decides not to kill her, but to expose her instead.
Once Amy decides she wants to escape from Desi, she has to put another elaborate plan in motion. Much like her first plan, it involves patiently waiting and carefully calculating every detail. Amy needs to ensure that when she returns, she has a plausible story for what happened to her, and that this story aligns with her fabricated disappearance. However, Amy's escape is more radical in that she actually kills Desi in cold blood. The fact that Amy is capable of doing so reveals her total lack of empathy and her ruthlessness. While Desi is creepy and controlling, he has never hurt her or anyone else. He has helped Amy with no questions asked, but when his presence is no longer convenient to her, she cuts his throat.
Amy's return is both Nick's salvation and an emotional catastrophe. Nick's name is now clear, and his innocence is established. However, he now has to figure out how he can live with Amy, knowing the truth about her. Nick has become shrewd and calculating enough to play the role of happy husband for the television cameras. However, when he hears the full story from her lips, he is horrified and repelled. The detail about Amy faking her pregnancy is particularly upsetting to him. This detail creates sympathy for Nick, showing him as a man who simply wants a happy, normal life with a loving family. Instead, he is stuck married to a monster.
Nick tries several strategies to get out of the situation. Ideally, he would like to see Amy brought to justice, but, as Tanner advises him, Amy still wields a lot of power here. Amy does have some vulnerabilities because there were some holes in her story, but Nick's claim of how she faked the whole thing will seem preposterous unless he can support it with strong evidence. Amy is still being her methodical self. She makes sure that Nick cannot record her confession and retains additional tools for blackmail.
Because Nick cannot take his story to the police, he thinks about more radical solutions, such as divorcing Amy or even killing her. Amy makes it clear that she cannot have her public image disrupted by a divorce. When she gloats over her apparent triumph, Nick nearly kills her. This moment is a turning point for Nick. Unlike Amy, he is not capable of murder. This confirms for the reader that he is the more humane partner in the marriage. Even though he is tempted to kill Amy, Nick is afraid of being like her.
More importantly, Nick feels a type of sickened attraction to Amy. He cannot imagine living without her. As evil and twisted as she is, she is still a part of him. Nick also feels a sense of responsibility towards her. Ironically, for the first time, Nick and Amy are honest with each other, and truly see the other for themselves. They are embodying more of what marriage typically means, as they no longer have any secrets from each other. While Nick still wants to contain Amy's recklessness, he is not ready to sever their lives together yet.