As the Rugrats' families prepare to embark on their vacation, excitement quickly transforms into turmoil when Stu unveils his unconventional choice of transportation—a dilapidated boat that leads them into treacherous waters. With a tropical storm looming ominously on the horizon, their journey takes a dire turn when a rogue wave capsizes the vessel, leaving everyone scrambling to safety on a life raft. As the boat sinks beneath the waves, tensions rise among the adults, who simmer with resentment towards Stu, feeling betrayed by his secretive decisions.
By morning, the families are washed ashore on a small, seemingly deserted island nestled in the South China Sea. Without clear leadership or direction, Betty steps up to guide the group, much to Stu's chagrin, especially after Didi intervenes to stop him from taking charge. As they survey their unfamiliar environment, Tommy, Chuckie, and the other children (excluding Angelica) embark on a mission to locate their idol, Nigel Thornberry, hoping his expertise can aid their return home.
Chuckie's adventure takes an unexpected twist as he loses his way and encounters Donnie Thornberry, who playfully steals his clothes, compelling Chuckie to wear the younger boy's shorts. Meanwhile, Eliza Thornberry ventures into the jungle with her chimpanzee companion, Darwin. They hear the desperate cries of Spike, the Pickles' family dog, which leads them to believe he’s searching for puppies. Together, they set out to assist him, only to discover that Spike is actually on a quest for human babies.
While navigating the hazardous jungle, Eliza and Darwin narrowly escape an encounter with Siri, an aggressive clouded leopard, which reveals the deeper mysteries of Spike's dilemma. As the Rugrats' families confront various challenges, they must unite to overcome the obstacles that await on this enigmatic island.
Fate takes a wild turn when Nigel sets out to reunite with his missing grandbabies, only to be transformed into a three-year-old after a freak accident with a coconut leaves him suffering from amnesia. Meanwhile, Chuckie and Donnie, who is played by Tommy Pickles, find themselves in a risky situation with Siri. Luckily, they manage to reclaim their clothes and escape her clutches in a harrowing chase that ends dramatically in a crater.
Angelica, with her impulsive tendencies, commandeers the Thornberry's all-purpose mobile communication vehicle, known as the commvee, which leads her to her sister Debbie. The duo embarks on an adventure that takes a turn for the worse when Angelica's reckless operations of the Thornberry's bathysphere cause the commvee to sink, sparking a frantic effort to rescue the babies and Nigel. Her determination pays off when she successfully locates the trio.
As chaos engulfs the island, Stu, who is also known as Phil, attempts to take charge by crafting a makeshift coconut radio to establish communication with Donnie and the other parents. In a twist of fate, Marianne Thornberry, Eliza's mother, unexpectedly encounters them while they pursue Donnie along the beach. Their journey leads them to Angelica, who inadvertently activates the bathysphere's radio, broadcasting the babies’ location. This culminates in a thrilling scene as Susie and Angelica tussle for control, ultimately resulting in the bathysphere crashing at the ocean floor.
After striking his head during the crash, Nigel regains consciousness and returns to his normal self. With a plan in place to salvage the commvee, Stu enables Marianne to utilize the automatic-retrieval system to rescue both Nigel and the babies just as their air supply begins to dwindle. With everyone safely reunited, the parents gratefully thank and forgive Stu for the turmoil.
As the group boards the Lipschitz cruise for a well-deserved vacation, the Thornberrys join the fun, delighting Debbie. Spike solemnly vows never to lose track of his precious babies again.
