The Octonauts embark on the biggest adventure ever! The crew is caught off guard by a volcanic eruption in the Pacific, but this single emergency soon turns into a global disaster when eruptions are triggered all across the Ring of Fire - a chain of hundreds of land and undersea volcanoes encircling the Pacific Ocean. As the Octonauts scramble to rise to the challenge of their multipronged rescue mission, Tweak has one last trick up her sleeve: the Gup-Z - a giant, untested new mecha Gup that will take the whole crew to operate.