When a 12-year-old chimney sweep is wrongfully blamed for being a thief, he makes a run for it and ends up jumping into a violent river. There he encounters a civilization of anthropomorphic underwater creatures. Before he can return to the surface and clear his name, however, he must help rescue his new friends, the Water Babies, from their nemesis. Featured voices include those of James Mason, Bernard Cribbins and Tommy Pender. The film starts and ends similarly to the book, though in the book Tom actually dies, and is only allowed above the sea on a temporary basis. The movie also adds a whole new subplot, involving a Killer Shark, an Electric Eel and the mythical Kraken, who decides whether or not Tom can return to the surface. There are also several invented characters, which Tom befriends on his quest: Jock, a Scottish lobster, Terence, an effeminate star struck Seahorse, and Claude, a foppish French swordfish.