One summer night on a Long Island beach, a friendly dolphin nudges thirteen-year-old Nita and summons her to the aid of a whale wounded by sharks. This is no ordinary whale, but a wizard named S'reee. Nita and her partner, Kit, rescue the: whale with their own recently acquired wizard powers, and S'reee begs them to help her conquer the evil Lone Power, who lies buried in the deepest part of the ocean, threatening to destroy the world. 
Nita and Kit agree to help S'reee by taking part in an ancient whale and shark ritual and becoming whales themselves. But Nita soon realizes that the ritual will lead her to a danger even more threatening than the end of the world. Does she have the courage to follow through on her promise?