When Cleo has a bout of carsickness on her way to a birthday swimming party, she is terribly embarrassed but her friend's mother helps her to forget the incident by encouraging Cleo to show off her talent for diving.
Geronimo Stilton, publisher of "The Rodent's Gazette" in New Mouse City, travels with his friends to the Ratlapagos Islands in search of treasure, and soon begin to suspect they are not the only ones involved in the quest.