The Investigation
The entire investigation into Amy's disappearance is ironic in that the investigation is supposed to serve the purpose of uncovering the truth about what happened to Amy. However, the investigation just spins the web of lies Amy has put in place. Every "clue" is actually part of her deception, and rather than leading the police closer to the truth, it takes them farther away. The investigation makes people more convinced of a lie (that Nick killed Amy), which is exactly the opposite of what it was supposed to do.
The Treasure Hunt
The treasure hunt that Amy has planned for Nick prior to her disappearance is ironic in a number of ways. Firstly, it appears to be a loving gesture, showing how much she cares about him and the romantic nature of their marriage. However, in reality, the treasure hunt is a way for Amy to taunt Nick and show him that she knows about his affair. The past treasure hunts have involved clues and locations that form part of the history of Nick and Amy's relationship. For this treasure hunt, she ironically inverts this pattern by having the clues and locations allude to Nick's affair with Andie. Finally, the treasure hunt is ironic because it should lead to a gift for Nick, but instead it leads to damning evidence against him.
Nick and Amy's Relationship After the Return
Ironically, Nick and Amy have a more intimate and honest relationship after her return than they did before her disappearance. Up until her disappearance, their marriage was built on lies, and Nick did not know the true nature of his wife. The two did not communicate regularly, and had less and less in common. After her return, there is total transparency between the two. When they talk, both Nick and Amy are naked, symbolizing how they are no longer hiding or holding anything back. Because Nick is the only other person who knows what actually happened, the two are bonded by a shared secret. Their relationship is an ironic parody of a happy marriage but it is more authentic and truthful than the relationship that previously existed.
Nick's Media Interviews
Nick's media interviews are ironic in that he says one thing while meaning the total opposite. Nick makes statements about how much he loves his wife, and how much he wants her to come home. The part about wanting her to come home is true, but by this point Nick is enraged with Amy, and fantasizes about killing her after her return. The interviews are also ironic in that they reveal that Nick is not totally unlike Amy. While he sees himself as the good man in counterpoint to her evil lies, he is also capable of being manipulative and deceitful. The interviews also display dramatic irony in that while readers know Nick is lying and tricking Amy, Amy herself does not. She is seduced by Nick's promises into returning home.
Amy's Pregnancy
Amy's pregnancy is ironic because rather than making her seem nurturing and caring, it confirms her cold and calculating nature. She does not get pregnant because she wants a baby or a family. She does so in order to trap Nick and know that she will always have control over him. A pregnancy also typically originates in either love or at least lust between a couple. But this pregnancy is engineered entirely by Amy, without Nick's knowledge or consent. Ironically, an act that usually speaks to the closeness between a couple reveals how alienated they are.
