The animated series centers on the life and adventures of the famous Geronimo Stilton, head of a media empire, a peaceful mouse and klutz extraordinaire, and his fearless young nephew Benjamin Stilton. Adventure always comes knocking on their door, launching them paws-first into capers in New Mouse City or in exotic locales around the world.

Journalist Cam Harrison and his niece Elle encounter a mermaid at a traveling circus in Mississippi and decide to free her from the grasp of Locke, the circus' evil leader.