In the opening scene, we meet Bobby (Demian Slade), a rebellious 14-year-old sporting leather attire and facial piercings, who narrates his family's story. His father, Frankie (Frankie Avalon), was once the legendary Big Kahuna, a celebrated professional surfer from Southern California and a teen idol in the 1960s. His mother, Annette (Annette Funicello), was a former Mouseketeer from the iconic Mickey Mouse Club, who left the glitz of Hollywood behind to start a life in Ohio. Now, Bobby grapples with the typical angst of adolescence, often clashing with his seemingly square parents. Frankie, now a worn-out car salesman, has traded in his surfboard for a suit, while Annette channels her restlessness into a flurry of shopping sprees.
The family decides to take a spring vacation to Hawaii, adding a stop in Los Angeles to visit their 20-year-old daughter Sandi (Lori Loughlin). Upon landing at LAX and renting a convertible, they drive past their old beach haunts to a pier where Sandi resides above a bait shop. Sandi has yet to inform her parents of her live-in surfer boyfriend, Michael (Tommy Hinkley), and only discovers they’ve arrived through a message on her answering machine. As soon as she sees them approach, she impulsively tosses out all of Michael's belongings, including his surfboard, creating chaos. Aware of Michael's presence, Frankie drags Bobby to find him while Annette comforts Sandi, who admits she's been living with Michael for the past six months.
On the beach, Frankie unintentionally destabilizes a set of surfboards belonging to a punk surf gang led by Zed (Joe Holland). Zed is drawn to Bobby but mocks Frankie for his outdated hairstyle, dubbing it a "hair helmet." Dismissing the gang's intimidating vibe, Frankie remains unfazed and walks away, only to inadvertently knock their boards over again. After gathering with Annette and Sandi, they leave for the evening.
As night falls, the family takes Sandi to her job at Daddy O's, a beachfront club. Annette, upon seeing a poster of legendary musician Dick Dale, urges Frankie to join her inside, but he initially declines due to their flight to Hawaii. Ultimately, curiosity gets the better of him, and they enter the club where Troy, a young surf bum, tries charming Annette, whose rejections lead to a tense encounter with Connie (Connie Stevens), the club owner and a past flame of Frankie. Connie showcases a tribute she created in honor of Frankie, showcasing his old surfboard along with memorabilia from his glory days, much to Annette's jealousy. Frankie, longing to relive old times, performs "California Sun" with Connie and Dick Dale, creating distress between him and Annette.
Their disagreements escalate when Annette, frustrated by Frankie’s nostalgia, storms out after realizing they’ve missed their flight. Back at Sandi's apartment, Michael arrives, hoping to rekindle their romance. However, they embark on a confrontation regarding Sandi's parents, ultimately resulting in Michael's departure. Meanwhile, Annette tries lifting Sandi's spirits by organizing a "pajama party" for her and her friends, which is interrupted by a group of punk surfers who are swiftly sent away by Annette and the girls.
A disheartened Frankie returns to Daddy O's and confides in Connie while nursing his sorrows. The following morning finds Frankie on a loft floor, surrounded by young surfers, including Mountain (David Bowe), who discuss their surfing escapades. Michael steps in, serving Frankie a drink to help shake off his hangover, revealing that he’s Sandi's boyfriend, which initially shocks Frankie but leads him to accept Michael's good nature.
At the beach, Frankie and Annette have a heart-to-heart regarding their marital struggles. In a moment of flirtation, Annette approaches Troy again without realizing Frankie is watching, leading to fractures in their relationship. Frankie seeks solace at Daddy O's, only to learn that Michael is Connie's son, which adds a layer of conflict to his emotions. Frankie checks into a hotel, grappling further with his failures.
As tensions rise, Bobby begins associating with Zed’s crew, even crafting cherry bombs. Frankie notices the fun that Michael and the other surfers are having but is overshadowed by Annette, who shows off her singing talents to Sandi and the other girls. Unfortunately, a rainstorm halts beach activities, forcing Frankie to improvise by selling ice cream, while he comes to appreciate Michael's potential in surfboard crafting.
That evening, as they ponder how to win back their loved ones, Frankie suggests a luau-themed beach party, which they attempt to get approved by the eccentric Harbor Master (Don Adams). They creatively pass it off as a ceremony honoring him, securing the needed permit. The beach party unfolds joyously, but Annette's jealousy reignites when Frankie is seen chatting with Connie again. Amidst their heated emotions, Frankie and Annette confront each other and finally apologize, leading to a rekindled connection.
Just then, Pee-Wee Herman (Paul Reubens) bursts into the party, performing a vibrant rendition of "Surfin' Bird" and prompting an ecstatic dance-off. As the festivities wane, Frankie reveals his deep-seated fear of surfing derived from a traumatic incident that occurred two decades prior. Tension escalates when Zed's gang crash the beach party, leading to a proposed surfing competition.
In a dramatic turn of events, Frankie faces his fear when Michael sustains a foot injury, leaving Frankie to surf in his stead during the competition. With his past haunting him, Frankie confronts a colossal wave, causing the other surfers to flee. However, he finds his courage, embracing the spirit of the Big Kahuna once more, and triumphs in the contest.
In the glorious final scene, Frankie and Annette, along with Sandi and Michael, celebrate at Daddy O's, where Sandi reveals her engagement plans. Bobby, now inspired, adopts his father’s style, signaling a bond formed through shared experiences. The film culminates with everyone uniting on stage to perform the closing number, "We'll Go on Forever."
