As night envelops Moominvalley, joy and music fill the air as the Moomin family and their companions gather around a lively bonfire atop a cliff. The flickering light creates a spellbinding atmosphere, yet unbeknownst to them, a pirate ship misinterprets the bonfire's glow as a signal and crashes onto the rocky beach below, forcing its crew to leap for survival. Among the fleeing pirates are Mymble and Little My, who get swept away by the turbulent waves.
With the dawn of a new day, Moomin finds himself grappling with conflicting desires: helping his mother with chores, going fishing with Snufkin, or indulging in a theatrical moment with Snorkmaiden. This inner turmoil highlights his ongoing quest for independence amid the constant calls for his attention. Suddenly, his eye catches Mymble floundering in the water, and without a moment's hesitation, he plunges into the sea to save her from peril.
After their daring rescue, the Moomins resolve to salvage whatever they can from the wreckage, gathering useful items like a mirror, books, a chest brimming with tropical seeds, and crates filled with fireworks. In their eagerness, they neglect to seize a hidden trove of gold that remains aboard the sinking ship. As the adventure unfolds, Little My, who has been observing from the ship’s crow's nest, makes a theatrical return to Moominhouse by riding on the back of a shark that has accompanied them from the wreck.
As twilight descends again, Snorkmaiden proposes they journey to the legendary Riviera, inspired by her idol Audrey Glamour and a magazine article. Thus, the Moomins, accompanied by Snorkmaiden and Little My, set off on their voyage, only to be caught in a fierce storm that tosses them about like playthings. Eventually, they wash ashore on a deserted island, where a peculiar box filled with thousands of verbal pests washes up alongside them. Unbeknownst to the group, the chaotic insects will soon unleash a whirlwind of havoc.
With the sun setting on the horizon, Snorkmaiden gazes longingly towards the dim lights of the Riviera. The next morning, buoyed by high hopes, the family embarks on the journey. Upon their arrival, they visit The Grand, the prominent resort hotel of the Riviera, where Moominpappa proudly introduces his family as "DeMoomin of Moominvalley." They are welcomed into a lavish Royal Suite, but soon find themselves struggling to blend in with the elite crowd.
As they search for their place, an unexpected friendship blooms between Moominpappa and Marquis Mongaga, an artist who appreciates Moominpappa's unique charm. Meanwhile, Snorkmaiden becomes infatuated with the allure of Audrey Glamour and the charming playboy Clark Tresco, much to Moomin's chagrin. As the family navigates this unfamiliar territory, they feel increasingly like outsiders. Ultimately, Moomin and Moominmamma decide to abandon The Grand's luxuries and retreat to their beloved beachside home, where they can rediscover a life that suits them.
Later that evening, as the serene beach captures their attention, Mongaga invites Moominpappa to see his prized collection of enchanting elephant sculptures that come alive in the candlelight. With a wistful air, he shares with Moominpappa his yearning to trade his glamorous lifestyle for a joyous, bohemian existence akin to that of his hosts. In a whimsical act, Mongaga replaces the statue of the town governor with one of his whimsical creations and soon immerses himself in the leisurely art of sculpture-making alongside the Moomin family. Days pass and Moomin is inspired to embrace his artistic side, leading him and Mongaga to create a captivating piece that embodies the spirit of Snorkmaiden.
The following day, fueled by jealousy, Moomin confronts Clark for Snorkmaiden's affection. Despite lacking sword-fighting skills, Moomin triumphs by resorting to an unexpected strategy – using the hilt of his sword to deliver a stunning blow. However, peace is short-lived as the hotel directors threaten to evict the Moomins, deeming their quirky nature unsuited for the establishment’s refined reputation.
Faced with a substantial bill for their stay, the family concocts a peculiar plan to settle their debt using Mongaga's prized sculptures. Unfortunately, the hotel management dismisses these artistic treasures, overwhelmed by their sheer number. Thankfully, Snorkmaiden steps in, using her unexpected casino winnings to cover the charges, significantly exceeding what is owed and generously allowing the hotel to keep the surplus.
As the day comes to a close, Snorkmaiden stumbles upon Moomin's sculpture of her as a stunning mermaid, and their embrace conveys an unspoken bond. In the days that follow, Moominpappa decides to gift homes to Mongaga's elephantine masterpieces, while Moominmamma opens her tropical garden for public enjoyment.
However, as the local authorities close in on Moominpappa, who has been wrongfully accused of stealing the town governor's statue, the family must make a hasty escape. In a bid to divert their pursuers, Moominmamma unleashes a swarm of bugs from her bag, overwhelming the officers with a barrage of verbal insults and curses. The scene erupts into chaos as the townsfolk attempt to restore order amidst this unexpected calamity.
As storm clouds brew overhead, the Moomin family navigates both literal and metaphorical treacherous waters. In a scramble to lighten their load, Moomin inadvertently ejects his cherished statue into the tumultuous sea. Now adrift, their small boat faces the furious onslaught of rampant greenery, which has broken free from its constraints and taken root all over the vessel. Fortunately, their dear friend Snufkin comes to their aid, guiding them safely back to shore, where the weary family can finally rest.
Upon returning to the familiar peace of Moominvalley, Moomin and Snorkmaiden share a tender moment atop a windswept cliff, a heartwarming reminder of the simpler joys in life - like flying kites with good friends Mymble and Little My as the sun sets on the horizon.
