After putting some Asterina starfish in the Kelp Forest where they don't belong, Splash, Ripple, and Tidy must get rid of them before the starfish eat all of the kelp. / Dunk, Bubbles, and Ripple don't believe Splash when he tells them about a mountain that spits out fire that can be found in the water really far down in the deep. To solve this mystery, the kids find Lu, who takes them into the deep to find a submarine volcano.