Nick Spitz, portrayed by Adam Sandler, is a dedicated New York police officer married to Audrey, played by Jennifer Aniston, who works as a hairdresser. Audrey has been longing for a romantic getaway to Europe, a trip that Nick promised her on their wedding day, but she has resigned herself to the belief that it will never come to fruition. On the occasion of their 15th-anniversary dinner, Audrey directly confronts Nick about their unreality, prompting him to fabricate a story that the trip is already booked, leading them to embark on a European adventure.
While aboard the plane, the couple encounters the wealthy Charles Cavendish, expertly portrayed by Luke Evans, who generously invites them to celebrate his elderly uncle's wedding on his family yacht. This lavish event is meant to mark the upcoming marriage of his uncle, Malcolm Quince, to Charles' former fiancée, Suzi, played by Shiori Kutsuna. The couple decides to ditch their crowded bus tour plans, thinking this yacht party would be a much better alternative.
Once on the yacht, Nick and Audrey meet an eclectic cast of characters: the ex-fiancée Suzi, Malcolm Quince's openly gay son Tobey, played by David Walliams, the celebrated actress Grace Ballard, portrayed by Gemma Arterton, Colonel Ulenga, played by John Kani, and Sergei, Malcolm's bodyguard, brought to life by Ólafur Darri Ólafsson. The charming but peculiar Maharaja Vikram, played by Adeel Akhtar, and race car driver Juan Carlos Rivera, depicted by Luis Gerardo Méndez, round out the group. However, the party takes a dark turn when Malcolm announces that only his new wife Suzi will inherit his wealth, suspecting that the others only wish to use him for his money. Tragedy strikes as the lights go out, and when they come back on, Malcolm is discovered fatally stabbed by his own dagger.
Amidst the chaos, Nick, who has falsely claimed to Audrey that he is an NYPD detective after failing his exams multiple times, takes charge and locks down the yacht for the investigation. Audrey puts her deductive skills to the test, theorizing that there must be at least two culprits involved in Malcolm's murder. The tension escalates when Tobey is later found dead in an apparent suicide, leaving behind a note that implicates him in his father's murder.
On reaching Monte Carlo, the guests are questioned by Inspector Laurent Delacroix, portrayed by Dany Boon, who harbors suspicions about Nick and Audrey's involvement. At the glittering Monaco Grand Prix, Nick and Audrey attempt to unravel the mystery, leading them on a trail of clues and confrontations. They learn from Sergei that years ago, Malcolm married the Colonel's fiancée while he was in a coma, which ended tragically with her death and an alleged stillborn child. The couple’s adventure takes a shocking twist when they witness Sergei's murder, propelling them into a desperate escape.
With stakes rapidly escalating and their own lives in peril, Nick and Audrey's relationship experiences turbulence as they confront secrets, lies, and the actual motivations of their fellow guests. Nick's deception about being a detective is uncovered, igniting a rift with Audrey, who seeks comfort from Charles. However, their bond is reignited when they discover the true love affair between Charles and Suzi, and they narrowly escape from a masked assailant who goes on to kill Suzi.
The couple realizes the interconnected lives of the guests, leading to a heart-pounding climax as they uncover more than one murderer among them. After confronting Malcolm's true heir, Grace, played by Gemma Arterton, and discovering her twisted lineage, they learn that Rivera, in his quest for revenge, poses an even greater threat. The climax erupts into a thrilling car chase, culminating in Rivera's explosive demise thanks to a returning tour bus, the very one Nick and Audrey used to consider boarding initially.
In a surprising yet gratifying resolution, Inspector Delacroix expresses gratitude towards the couple and hints at helping Nick attain the detective title he has long aspired to. The film concludes with Nick and Audrey setting off to continue their long-awaited vacation aboard the luxurious Orient Express, courtesy of Interpol, leaving behind a whirlwind of mystery and newfound adventure in their wake.
