For the last three months, Mr. Moseby, the former manager of the Tipton Hotel in Boston, has been enjoying his new position as cruise ship manager aboard the S.S. Tipton. When London Tipton, the ship's owner, arrives on board, Mr. Moseby tells her that she is not there for vacation, but to attend Seven Seas High School, the onboard school program, per orders from her father. Much to his dismay, Mr. Moseby encounters Zack and Cody, his foils from the Tipton hotel in Boston, who surprise him when they announce that they too will be attending Seven Seas High, thanks to Carey's employee discount. Mr. Moseby is so overwhelmed by the news, he jumps overboard.
After being rescued, Moseby reluctantly has to deal with the fact that Zack and Cody will be on board for the semester. Meanwhile, at check-in, London claims to insist on no special treatments--while cutting to the front of the line. Another new female student Bailey, a small-time farm girl, arrives on board, but quickly disguises herself as a boy.
Later, Zack and Cody's mother, Carey, gets emotional saying good-bye to the boys. Cody remains strong, but Zack surprisingly breaks down crying because he'll miss his mommy.
In her cabin, London mistakes her new roommate, Padma, for the maid. London doesn't want to share a room, so she bribes Padma to drop out of school so she can have her own room.
Zack and Cody are assigned to different rooms. Cody is bunking with Woody, a slob who's even messier than Zack. Bailey, meanwhile is assigned to bunk with Zack and tries to pass herself as a guy. To keep up her charade, she decides to put up a rope to divide the room and comes up with a bathroom schedule.
The students take a tour of their new rooms, including the marine biology lab. Zack, Cody, Bailey and Woody stay behind to see the octopus. When Zack gets along with Woody, Zack and Cody decide to switch roommates. Woody picks up the octopus who squirts ink on him, Zack, Cody and Bailey, who accidentally throws the octopus out of the porthole. Cody has to climb out the porthole to retrieve the octopus, and his pants fall off during the process revealing his Share Bears underwear.
While cleaning up from the octopus ink in their room, Zack discovers Bailey's secret--that she's a girl. Bailey confesses that she applied as a boy because all the girl positions were filled and she really wanted to attend Seven Seas High to escape her farm life. Bailey begs Zack to keep her secret, but when Cody walks in on them and sees them holding hands, Zack says he's not switching roommates.
In the arcade, Zack, Cody, London and Bailey are playing a video game with headphones when they miss the announcement about a safety drill being conducted. After hearing the safety bells, they mistakenly believe the ship is sinking. They find lifejackets and scramble out the first exit they find, only to end up in the hot tub, where Bailey is exposed as a girl when her baseball cap comes off.
Zack explains to Ms. Tuttweiller, the school director, and Mr. Moseby the reasons Bailey masqueraded as a boy to attend Seven Seas High. Ms. Tuttweiller says that while Bailey's application is impressive, unfortunately, there's no cabin to put her in so she can't stay onboard and attend the school. When London brags that she has no roommate of her own, Mr. Moseby assigns Bailey to be London's new roommate, much to London's dismay.
Later, Ms. Tuttweiller finds a note that London is running away. Mr. Moseby says that London can't escape from a boat in the middle of the ocean... that is, until a helicopter arrives to take her away.
(To be continued...)