The Unhoneymooners recap

After nearly everyone at Ami and Dane's wedding is struck by food poisoning, the only healthy members of the wedding party are Ami's twin Olive and Dane's brother Ethan, who strongly dislike each other. They take the couple's nontransferable Maui honeymoon by pretending to be newlyweds. Encounters with Olive's new boss and Ethan's former girlfriend force them to maintain the act, while shared adventures expose the attraction beneath their hostility. They return as a real couple, but Olive then discovers that Dane has been cheating on Ami. Ethan refuses to believe his brother could be responsible, and his distrust breaks the new relationship; Olive's accumulated lies also damage her work prospects. When the truth about Dane is confirmed, Ami ends the marriage and Ethan recognizes how badly he failed Olive. He makes a sincere apology, Olive gives him another chance, and the epilogue leaves them happily committed to each other.

Olive Torres arrives at her identical twin Ami's wedding expecting her usual bad luck to continue. Ami has won or negotiated nearly every part of the celebration, including a nontransferable honeymoon in Maui. Olive's chief irritation is Ethan Thomas, the groom Dane's older brother, with whom she has clashed since they met. During the reception, almost every guest who eats from the seafood buffet becomes violently ill. Olive is spared because of an allergy, and Ethan because he refused the buffet. With Ami and Dane too sick to travel, the twins press Olive and Ethan to take the trip under the newlyweds' names rather than waste it. The pair reluctantly agree, setting off together while still insisting that they cannot stand each other.

In Maui, Olive and Ethan check into the resort as Ami and Dane and establish rules meant to keep them apart. Their plan fails when Olive runs into Mr. Hamilton, the employer at the job she is about to begin, and lets him believe she has just married Ethan. They also encounter Ethan's former girlfriend Sophie and her partner, giving Ethan his own reason to maintain the fiction. To avoid exposing the fraudulent booking or embarrassing themselves, Olive and Ethan must perform as affectionate newlyweds in public. The forced cooperation softens some of their assumptions about one another, even as competitive excursions and old grievances keep their exchanges sharp.

Olive and Ethan spend more of the vacation together, sharing meals and resort activities while sustaining their invented marriage for the people they know. Away from their siblings, their hostility gives way to candid conversation and obvious physical attraction. Olive learns that Ethan's cool manner does not match every conclusion she formed about him, and he sees that her expectation of bad luck hides vulnerability rather than simple negativity. They kiss and begin a genuine romantic and sexual relationship, making the honeymoon feel less like an inconvenience. Yet their history remains unsettled, particularly the conflicting stories surrounding Olive and Dane's early interactions and the reason Ethan has judged her so harshly.

As the trip continues, Olive and Ethan acknowledge that what has developed between them is real. Their discussions reveal that Dane told Ethan Olive had behaved inappropriately toward him, while Olive remembers Dane as the person who crossed a boundary. The discrepancy plants doubt about Dane but also shows how readily Ethan accepted his brother's version. Encounters with Mr. Hamilton and Sophie strain the false-newlywed performance, and the truth about whose honeymoon they are using threatens embarrassment. Despite those complications, Olive and Ethan decide not to treat their intimacy as a temporary resort affair. They return to Minnesota intending to continue the relationship in ordinary life.

Back home, Olive tries to begin both her job and a real relationship with Ethan. She then finds persuasive evidence that Dane has been unfaithful to Ami, not as a single mistake but as a pattern concealed during their courtship. Telling her twin is painful, and Dane relies on denial and Olive's known dislike of him to defend himself. Ethan also rejects Olive's conclusion and stands by his brother. His refusal to consider her account repeats the distrust exposed in Maui and leads to a bitter breakup. At the same time, the lies Olive told about being married during the honeymoon catch up with her professionally, leaving her relationship, employment, and bond with Ami under severe strain.

Additional evidence establishes that Dane repeatedly cheated, vindicating Olive's warning. Ami ends the marriage and begins recovering with the support of her twin and extended family. Ethan is forced to recognize both his brother's deception and his own readiness to disbelieve Olive. He approaches Olive with a direct apology and takes responsibility for choosing family loyalty over the facts and over trust in her. Although his rejection caused real damage, Olive sees that he has confronted it honestly and agrees to give their relationship another chance. The epilogue finds Olive and Ethan securely together, their supposed honeymoon now the origin story of a genuine partnership rather than an impersonation. Ami, no longer tied to Dane, is moving forward with her family beside her.

Olive returns from Maui in a real relationship with Ethan, but the happiness collapses when she uncovers evidence that Dane has repeatedly been unfaithful to Ami. Ethan initially trusts his brother and treats Olive's accusation as another product of her hostility toward Dane. The argument ends Olive and Ethan's relationship, while the false identity she maintained on the honeymoon also contributes to trouble at her new job. Further evidence confirms that Olive was right. Ami leaves Dane, and Ethan confronts both his brother's conduct and his own failure to believe Olive. He apologizes without excuses and asks for another chance. Olive does not erase the hurt, but she accepts that he now understands it and chooses to rebuild their relationship. By the epilogue, they are securely together and able to regard the disastrous borrowed honeymoon as the unlikely beginning of a lasting partnership, while Ami has moved out of her dishonest marriage and is rebuilding her own life with her family behind her.