McKenzie, "Mack," and her boyfriend, Brady, surf near her grandfather's beach hut in Waikiki. Shortly thereafter, Mack walks in on her grandfather and Brady watching their favorite film, a 1960s musical titled
Wet Side Story, in which surfers and motorcycle bikers battle for the privilege to hang out at Big Momma's beachside restaurant. When Mack's aunt comes by, she explains to Brady that before Mack’s mother died, she promised Mack’s mother that Mack would attend a private school, and that she will be leaving the next day. Mack asserts that although leaving is not her choice, she feels it is what she has to do since it is what her mother would have wanted. She subsequently tells Brady that they must break up. Before Mack leaves, she decides to surf an impending 40-foot wave on her family's surfboard. Brady gets on a jet ski and goes after Mack, but they both get swept away, eventually landing on another beach. They soon realize that they have been swept into the realm of the
Wet Side Story film. Seizing the moment, Brady joins the film's cast in singing, to Mack's dismay. Brady relents and informs Mack that there will be a storm and giant wave that should bring them back home at the end of the film. They go into Big Momma's and introduce themselves to the surfers just before the bikers appear and start the surf and turf war. Mack and Brady are then invited to a party at Big Momma's later that night. That evening, Mack and Brady argue while the film's female lead, Lela (one of the biker girls), sings on stage. Tanner, the male lead and one of the surfer boys, falls in love with Mack after she bumps into him, whilst Brady catches Lela, whom subsequently falls in love with him, as she falls off the stage. This interferes with the film's plot, as Lela was supposed to fall into Tanner’s arms. Brady and Mack determine to make Tanner and Lela fall in love to fix things. Brady also tells Mack about the film's villains, Les Camembert and Dr. Fusion, who plan to use a
weather modification machine to make the surfers and bikers leave so they can redevelop Big Momma's into a beach resort. Lela and Tanner express their love for Brady and Mack, who subtly suggest to them that there may be someone else they are really meant to be with. That night Mack joins Lela and the other biker girls for a sleepover, while Brady hangs out with Tanner and the surfer boys at Big Momma's. Brady and Mack's modern relationship views come into conflict with those of the 1960s; they fail to make progress on getting Lela and Tanner together. The next night, Lela tells Mack that she would like to surf. Mack and Brady realize that they are morphing into the film when Mack falls into the water and her hair does not get wet. They begin to sing involuntarily before being captured by Les Camembert and Dr. Fusion and taken to the lighthouse lair. Lela and Tanner fall in love with each other and soon realize that Mack and Brady have been kidnapped. They convince the bikers and surfers to team up and save Mack and Brady. Meanwhile, Mack admits that she is glad that she ended up in the film and does not have to attend private school. When Mack says she thinks Lela is braver than her, Brady denies that, saying that Mack is the bravest girl he knows. The surfers and bikers free Mack and Brady and destroy the villains' machine. The film's plot returns to normal, and Mack and Brady realize they are able to return home. After bidding farewell, Mack and Brady get on the surfboard and returns to the real world, where no time has passed since they left. Mack successfully surfs the 40-foot wave. Mack's aunt is upset about her delaying their flight but accepts her decision to spend the rest of the year with Brady. In a
post-credits scene, Lela, Tanner, Butchy, Seacat, Cheechee and Giggles wash up into the real world. A modern-day surfer thinks they are lost and allows them to use his cell phone, which they marvel at as they attempt to use it. ==Cast==