It's summer vacation, and the Wonder Pets rescue a young circus lion named Cubby from falling off a circus train. The Penguin Ringmaster is so impressed with the Wonder Pets that he offers them jobs at the circus. But Linny hates this as much as Tuck and Ming Ming and wishes they were heroes again instead of circus performers. But after they rescue the animals from a trapeze they start to miss their home and decide to be heroes again.