Jim works as an innkeeper alongside his friend, the mouse Gran. One day, a mysterious man visits the inn and leaves a map behind. The map depicts an island with a treasure. Consequently, the duo sets off in their small boat, attempting to fulfill their dreams and leaving the inn far behind. However, it seems more people know of the map, as they cross paths with Captain Silver and his band of wild pirates. Jim, Gran, and their new friend Kathy try to beat them in the ensuing treasure hunt.