London, Zack, Cody and Mr. Moseby set sail on the S.S. Tipton for their semester at sea. London convinces her roomate to leave the ship so she can have a room to herself. Cody finds himself sharing a room with Woody, who is very messy, and Zack shares a room with Bailey, who is a neat freak. Nobody knows that Bailey is a girl who disguised herself as a boy in order to gain a position on the ship after she found that there were no more vacancies for girls. Zack and Cody agree to switch roommates, but Zack changes his mind after he finds out that Bailey is a girl. After everyone else eventually finds this out Bailey is allowed to stay, filling the position vacated by London's ex-roommate, and Bailey becomes London's new roommate. This is the last straw for London and she escapes to Parrot Island via helicopter.

The boys plan to have an all-guys weekend with their dad, but a surprise visit from their mom ruins it. When Kurt and Carey get a show on the ship, Mr. Moseby says they can stay on board, but worried their parents will permanently stay on the ship, the twins hatch a plan to sabotage their parents' show. Meanwhile, London tries to find the perfect belated birthday gift for Mr. Moseby by following him around all day. In the end, London makes Mr. Moseby very happy that he got a present from her because even his own mother forgot his birthday.

Carey joins the boys while they're in Japan when she's selected to star in a soda commercial by a businessman who's taken a liking to her when he saw her perform at the Tipton. Shooting the commercial is difficult enough since the soda is flavored with shrimp and tastes awful. Things get worse when Zack smashes an expensive camera and the family has to pay for it by becoming tasters at the soda factory. Meanwhile, Woody is able to defeat a sumo wrestler in the ring to win an unlimited ship gold card. However, having lost his confidence, the wrestler continuously hangs around Woody, getting him annoyed to the point of facing him in the ring again in hopes he finally leaves the ship. Also, London does everything she can to avoid going to the dentist.

Mr. Moseby announces that London's dad, Mr. Tipton is selling the ship and that it will be dismantled within a week.