Timmy is at the beach and he’s bored silly. He, Cosmo, and Wanda set off to explore the deep, and everywhere they go, but Cosmo seems to be hated by every single fish. Soon, they end up in the lost city of Atlantis. Timmy appeals to Atlantis’ leader, King Greg — if he can show good cause why Atlanteans should be happy beneath the sea, Cosmo will be set free. Will Timmy save Cosmo?