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.
When the S.S. Tipton makes a special trip to pick up London from Parrot Island, Bailey, Moseby and Woody find themselves in jail because all the parrots left for Seal Island after Tipton Industries cut down all the trees. It's up to Zack and Cody to get them out of it but Zack and Cody end up in jail along with the others, and Bailey has to use her pig, Porkers, to rescue them. Zack and Cody fight for Bailey and Zack lets Cody have her after finding out about her ex-boyfriend Moose and seeing she has too much "baggage".
Bailey is mad that London is hogging all the space in their cabin, so she makes up a "Sea Snark" attack, but later feels guilty and tells her the truth. Meanwhile, when Zack uses up both his and Cody's meal cards buying things for all of the girls on the ship, they go broke. To make up for it, Moseby puts them to work. Because of that, Zack thinks that Cody should win the yo-yo contest for its $1,000 prize, but Cody finds himself up against the pro, Johan Yo.
Zack has a crush on a cute passenger named Violet, but must deal with her wealthy "boyfriend" Ashton and snooty mother who will do anything to keep Zack and Violet apart. Meanwhile, Cody referees an intelligence test between London's dog Ivana and Bailey's pet pig Porkers. The episode includes plot elements from the 1997 film Titanic, where Jack was framed for stealing the "Heart of the Ocean" necklace.
London and Bailey are on a mission to prove that Miss Tutweiller is dating Mr. Moseby after overhearing a conversation between the two. Meanwhile, Zack convinces Cody to sneak out after curfew to catch the Starlight Follies show on the ship. When they finally make it past the security guard and into the show, they become convinced that their teacher, Miss Tutweiller, is one of the showgirls by seeing her heart shaped anklet in the show, and during class, so Zack sends Bailey and London undercover as two showgirls to find out.
The ship is struck by lightning when it crosses the International Dateline, which places Cody in the same day over and over. He tries to use each day as a chance to let Bailey know how he feels about her, but something gets in the way every time. It's then up to Cody to divert the ship from the lightning to set them back on the right course.
The S.S. Tipton visits Greece. While they are there, Bailey crushes on the tour guide, which makes Cody jealous. To impress her, Arwin's cousin, Milos, gives him a replica of the ancient amulet of the Greek goddess Aphrodite to give as a gift to her, but in a mix up, he ends up getting the real one. Meanwhile, London has to write a speech for her father, who is funding a new exhibit, but finds it very difficult, but then has a dream about Greek history, which inspires her.
The class has a school project to complete and Cody chooses Bailey to be his partner, disappointing Zack who had hoped to get Cody to complete his and Woody's project for them. After Bailey tells London that she has partnered with Cody, London teams up with Zack and Woody. Cody is trying to catch a famous sea monster, but keeps failing and disappointing Bailey. Zack tries to sabotage Cody's project. However, his own project turns into a monster when London pours a smoothie into their plant project, causing it to grow and eventually trapping Zack, Woody, and London. The sea monster shows up at the end of the episode.
Chelsea, Barbara, and Bob visit the S.S Tipton. Cody is worried about how he's going to tell Barbara about his feelings for Bailey, but Barbara has to dump Cody because she and Bob are now dating. Right before Cody tells her about Bailey, Barbara tells him about her and Bob. To make Barbara jealous, Cody tells her that he and Bailey are also dating, thinking he can get away with the lie because Bailey is off the ship, but she returns early. London tells Chelsea that her room is her shoe closet, and that Woody is her servant. Woody agrees to help her because he has a crush on Chelsea. During movie night, Cody tries to make Barbara think that he and Bailey are dating, but Bailey eventually finds out. Cody apologizes and Bailey forgives him and says if he wanted her to be his pretend girlfriend, all he had to do is ask. To show it, she tickles him, wraps her arms around him, and finishes with a kiss on the cheek (causing Cody to faint) saying that would have made Barbara really jealous. Chelsea finds out that London is just a regular student, but instead of telling everyone, tells London she will tell everyone that London was "abducted by aliens" instead.
When Cody and Kirby don't allow Zack to bungee-jump off the side of the ship, the brothers accidentally knock Kirby off the ship, but Kirby lands in the hot tub. To make it up to him, Zack and Cody tutor Kirby so he can pass his high school equivalency exam to earn a better job. Meanwhile, London embarrasses Bailey on her internet show in a new segment called "Boo You!"
Zack and London play matchmaker for Mr. Moseby and Ms. Tutweiller, but with little success. Eventually, they get Moseby and Tutweiller together, and although they have an argument, they remain together. Meanwhile, Cody tries to impress Bailey by acting like someone else based on her dating test results. However, what Cody doesn't know is that some of her answers were for fun, while others were true.
When the ship stops in India, Cody takes Zack with him to visit his guru, a Swami who lives in the top of a mountain who charges high prices for everything he sells. Eventually, Zack and Cody run out of money and join the Swami's worldwide call center. Meanwhile, Mr. Moseby is having computer problems and is trying to contact the call center for help, but without any success. Padma, who was originally London's roommate on the ship, but left after London bribed her, asks London to help convince her mother that she was still at sea. It is later shown that the help center Moseby was calling was run by the Swami, who used an American accent.
Maddie Fitzpatrick visits the S.S. Tipton and gains a new friend in Bailey. Prince Jeffy of Linchtenstamp, who's only 8 years old, falls in love with Maddie and forces her to marry him. However, Zack challenges the Prince to a joust, with Maddie being the prize. Zack beats Prince Jeffy on a bouncing ball and using a water noodle weapon. Also, Zack finally gets his long-awaited kiss from Maddie.
The ship docks near Rome and London falls for a young, handsome musician named Luca while playing in the streets. Later, as Bailey searches for her money belt key, she overhears that Luca and his uncle, Marco, are actually con men and had already conned London for twenty thousand dollars. Bailey talks to Luca and finds out that he actually doesn't want to be a con man and really likes London. So, they hatch a plan to get the money back from his uncle which includes Bailey dressing up as Naomi Wyoming, a parody of Hannah Montana. Meanwhile, Zack and Cody get themselves hired by Chef Gigi so they can eat at her restaurant. At the end, Cody is fired, but Zack enjoys a delicious meal with Gigi.
A famous hypnotist visits the S.S. Tipton and accidentally hypnotizes London to act like Bailey, which gets her really annoyed. Meanwhile, Harvard's Dean of Admissions, Monroe Cabbit, is also visiting with his daughter Olivia. Cabbit is fond of Cody, but thinks lowly of Zack, although Zack wants to date Olivia. Since Cabbit does not approve of the relationship, Zack and Cody concoct a plan where Cody will pretend to date Olivia, which Cabbit approves of, but Zack will actually be the one who goes on the date.
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.
After Kirby injures Moseby, Connie takes over Moseby's work and breaks a boat in a bottle intended as a gift for the captain. Everyone tries to comfort Moseby, but none of them do any good. Moseby overhears mention of a problem with the boat and thinks there is a problem with the full-size ship. London eventually fixes the boat in a bottle. Moseby falls down the stairs and injures everyone except London. Finally, Moseby accidentally breaks the boat and doesn't have enough time to repair it.
Hannah Montana boards the S.S. Tipton on her way to a concert performance in Honolulu. To impress Bailey, Cody desperately tries to get tickets to the show. Meanwhile, the Russo's are still aboard the ship on their vacation in which Alex pulls a prank on Justin by putting blue dye in the hot tub, making him turn blue, for which Mr. Moseby blames Zack, while Max tries to impress London with his magical suitcase.