The Octonauts must find a way to hold back hungry swarms of coral-eating starfish to save a new friend's fragile reef home.

In this film's adventure, a volcano erupts suddenly, suddenly awakening the Pacific Ocean floor of hundreds of volcanoes composed of the "ring of fire", this sudden event quickly turned into a global catastrophe. The volcanic clusters that are about to erupt en masse threaten the horned whales washed ashore by the tsunami, the cap penguins living in the volcanic islands, the equipment of the small column maintenance station, the food planted by plant fish in the marine farms... Not to mention the plants and animals that live in the crater all year after year!