Twenty young lobsters graduating from Lobster School emerge from the depths of the Gulf of Maine. They colonize the "Black Rocks," three small rocky islands a quarter of a mile off York Harbor Beach. They are very excited, as they are free for the first time from parental supervision. Disaster strikes the following morning when they realize that Lancelot Lobster is missing. He is always ravenous and they assume that, despite all the warnings in school, Lancelot might have been tempted to enter a lobster trap. Their adventures begin: a dramatic rescue, a lobster hunter, a mussel-eating fox, smugglers, shipwrecks, a ghost circus, submarines, lobster boat races, a misunderstanding in a lobster bar, and the heroic rescue of an entrapped whale.