Emerald's class are spending the day sea combing-picking up human rubbish that ends up on the ocean floor. When Emerald finds a precious teddy lying in a clump of seaweed, she's tempted to keep it for herself, but the tag says it belongs to a human called Jack.

Emerald asks her land-loving friend, Isadora Moon, and Isadora's cousin, Mirabelle, to help her return it and together they embark on an exciting adventure across the land and sea!