A nuclear strike by Cuba on the southeastern United States not only sunk most of the major cities like Atlanta, but the radiation mutated the local sea creatures. At first they were mindless monsters called "Sea Devils", but after 40 years they had evolved into human-like being and modified the sunken cities into homes for their people. The Sea Devils split into tribes by their species, Shark Tribe, Eel Tribe, Whale Tribe, etc. and made a society. They constantly have to fight with humans who still see them as monsters, and many of them, even their children, are shot on sight by fishermen. A small group of them interact with the surface world, led by evolved manta ray Redfin, to try and make a better life.