On a massive luxury cruise ship while at sea, the loyal butler Suguru, and a mysterious woman named Chizuru cross paths as they try to uncover a murder-mystery that occurs on the ship.

Suguru, a devoted butler of a luxurious cruise ship, sees his life turned upside down the day he encounters Chizuru, a woman who claims that their respective partners are on the verge of cheating. Chizuru tries to convince him that they have to stop the cruise and go back to Japan to prevent their partners from cheating when one night, the two of them, along with five other passengers, witness a dead body floating in the rooftop pool. Strangely, all but Suguru pretend they haven't seen anything. While trying to uncover this mystery, Suguru and Chizuru are gradually drawn to each other.