Timmy Turner is at the beach and he is bored silly so he, Cosmo, and Wanda set off to explore the deep, and everywhere they go, Cosmo seems to be hated by every single fish. Soon, they end up in the lost city of Atlantis, and Cosmo is taken captive when it is revealed it was he who sunk the city long ago. 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?