During his explorations of the vast ocean, the courageous town mouse known as Gamba encounters a distraught child mouse named Chuta. The young mouse tells a heartbreaking tale of how his family and community were mercilessly slaughtered by a group of weasels who reside on a nearby island. Despite seeking assistance from a group of bold ship mice, Chuta is ultimately abandoned once they realize that the notorious weasel leader, Noroi, is responsible for the tragedy. Moved by his empathy for Chuta's plight, Gamba makes a solemn promise to rescue the island, the young mouse's loved ones, and any remaining survivors. Alongside a team of fellow supporters, Gamba embarks on a challenging quest to confront and defeat Noroi and his pack of malevolent weasels.