After their uncle breaks his wing Goro and Kiyoko go to spend the summer with their human friends Arthur and Samantha, and their parents at an old outpost in Elysium province. Goro wants to be a marine biologist, and when he finds out about Utopia Colony, the abandoned underwater colony of the coast, he decides he's going to visit it. Unfortunately the only sub at the outpost belongs to the grouchy old handyman, and he won't let anyone near it. Goro and Samantha put their heads together to figure out a way to visit Utopia Colony, but then wish they hadn't.