Gidget's sun-soaked Hawaiian vacation kicks off when her father reveals a two-week stay in Hawaii, a plan that promises adventure, sun, and a chance to stretch her young heart. On the plane to the islands, Gidget Deborah Walley crosses paths with Abby Stewart Vicki Trickett and her parents, including the dazzling Eddie Horner [Michael Callan], a popular dancer who instantly draws attention from the group of boys aboard. Still, Gidget misses her steady boyfriend Jeff "Moondoggie" Matthews [James Darren], and the prospect of a long, exasperating separation gnaws at her as she tries to fit into this new social orbit. The stage is set for a clash of worlds: a spirited surfing culture, glamorous nightlife, and a romantic triangle that could redefine her idea of growing up.
That first night in paradise, Abby invites Gidget to join her and Eddie, pulling her into a glittering circle of flirtations and competitive camaraderie. As Gidget begins to shine with the other boys and especially with Eddie, she unintentionally becomes Abby's rival, sparking a spark of jealousy that she hadn’t anticipated. The next day, Gidget’s confidence surges as she masters the surf, and just as Jeff arrives, Eddie unexpectedly kisses her, throwing the boy who loves her into a quick, heated confrontation. The dinner scene that follows amplifies the tension: Jeff comes to terms with Abby’s circle, Gidget retaliates by flirting with Eddie, and the rivalry deepens as the days roll on through water-skiing and other seaside escapades.
When the gossip mill starts to churn, the trouble escalates. Abby, driven by envy and a bruised ego, spreads a rumor that Gidget has slept with Eddie and other guys, a lie that travels through the hotel and stirs resentment between the two families. The rumor triggers a chain reaction at home too, as Gidget's mother Dorothy Lawrence [Jeff Donnell] and Abby's mother Mitzi Stewart [Peggy Cass] confront the deceit and misbelief swirling around them. The adults’ arguments echo the youngsters’ quarrels, and for a moment it seems like the whole vacation could fracture into two equally stubborn camps. Yet the adults manage to navigate their own misunderstandings, and a fragile peace edges its way back into the picture.
At the evening Lūʻau, Abby confesses the rumor to Jeff, admitting that it’s a lie. This admission helps to thaw the frost between Jeff and Gidget, and they quietly begin to repair what the rumor fractured. The two lovers reconcile on the beach, choosing honesty and patience as they prepare to set things right with the adults. Yet misunderstandings persist, as Gidget fears her parents might be having an affair with Abby's, while her own parents worry that Gidget might vanish or lose her way. A flurry of mistaken assumptions kicks up the final comic storm, until everyone gathers in Gidget's room and reality finally settles—the young couple is simply waiting in the adjacent suite, while the adults sort through their own squabbles.
In the end, order returns to the sunshine-soaked drama. The next day, as a playful punishment for the rumor-spreading, the guys drag Abby into the ocean and place her on Gidget's surfboard. Abby clings on in a moment of legitimate fear as the surf rolls in, while Gidget and Jeff ride the waves together, a quiet celebration of trust, youth, and the hard-won clarity that comes from a summer spent learning what it means to belong to someone you love.
