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We meet Nick, a New York police officer who desperately wants to be a detective but keeps failing the test. He’s married to Audrey, a hairdresser who dreams of visiting Europe—a promise Nick made at their wedding but has yet to fulfill. After their 15th wedding anniversary dinner, Audrey calls him out on it, only for Nick to surprise her with the news that he’s actually booked the trip. (He totally hasn't—but sometimes you gotta spend thousands of dollars to keep up a lie.)

On the flight, Audrey meets billionaire Charles Cavendish, who invites her to a gathering aboard his family’s yacht. When Nick hears about this, he’s like, “No way. I have a whole thing planned.” But when that plan turns out to involve a packed tour bus, he gives in.

Aboard the yacht, Nick and Audrey meet quite the cast of characters: Malcolm Quince (Cavendish’s billionaire uncle), Suzi (Cavendish’s ex-fiancée and now Quince’s wife), Quince’s son Tobey, actress Grace Ballard, a colonel and his bodyguard, a rapper, and a race car driver.

Later that evening, Quince arrives and announces that Suzi—his new wife—will now be his sole heir, cutting everyone else out of the will. Naturally, this does not go over well. Just before the new will can be signed, the lights go out—and when they come back on, Quince is found stabbed through the heart.

Nick jumps into detective mode and tells everyone to stay on the yacht. That night, Tobey is found dead in what looks like a suicide.

When they arrive in Monte Carlo, a local investigator boards the yacht to question everyone. The other guests point fingers at the “random Americans.” The investigator tells Nick and Audrey he knows they’re guilty and promises to prove it.

At the Monaco Grand Prix, Nick and Audrey begin their own investigation to clear their names, interrogating the other guests.

That night, the colonel’s bodyguard lures them to his room and drops a bombshell: Quince once married the colonel’s fiancée while the colonel was in a coma. She later died in childbirth. Just as things get juicy, someone knocks. Nick and Audrey hide, and when they come out, the bodyguard has been shot—he dies before naming the killer.

Audrey is shaken when a news broadcast reveals that Nick isn’t really a detective. She storms off and is picked up by Cavendish, who urges her to leave Monte Carlo immediately.

Eventually, everyone winds up at a lake. Nick and Audrey reconcile and start to suspect that Cavendish and Suzi are romantically involved and conspiring to split Quince’s fortune. While fleeing a masked attacker with a blow dart, they run into Carlos, the race car driver. Suzi is killed with a dart, and Nick and Carlos chase the killer but lose them.

Nick and Audrey head to Quince’s mansion to confront Cavendish—only to find him poisoned.

They call the investigator and gather the remaining guests, but everyone seems to have an alibi. Nick and Audrey then reveal that Grace, the actress, is the mastermind. She’s actually the daughter who was believed to have died in childbirth. She convinced Tobey to kill their father and then killed him herself. When she tries to escape, Nick shoots her in the arm.

But the mystery isn’t over—Carlos is revealed to be the second killer, seeking revenge on Quince for the injuries that left his father disabled. Carlos takes the investigator hostage and tries to escape in a car, but Nick and Audrey stop him—with help from that overcrowded tour bus they skipped earlier.

In the aftermath, the investigator thanks them and offers to help Nick finally earn his promotion. The couple continues their European adventure.