After losing a math contest to Buster when he cannot get over a question that he got wrong, Brain decides to start being funny instead of smart. Although they want to go to Aqualand, an exciting water park, Arthur, Buster, Binky, D.W., Sue Ellen, and Brain are instead brought to the beach, where Arthur's father tells them about Ocean Zone and leaves them to find it. They have fun at the beach and realize that the beach is Ocean Zone.