Aquaman is exposed to a radioactive substance that turns him into a prehistoric sea creature from which he evolved. In order to cure him, Superman and Wonder Woman, inside the Supermobile, are shrunk down to microscopic size and sent within the creature's veins to attempt to give it another dose of radiation in the hopes that it will reverse the effects of the radiation and return Aquaman to normal. In the meantime the rest of the Super Friends have to do whatever they can to limit the creature's destructive nature all over the city.