Gamba, a town mouse with a brave, adventurous spirit decides to go on an adventure to discover the ocean. On his way, he meets a troubled child mouse, Chuta. He says his family and other mice have been killed by a clan of weasels living on a nearby island. Chuta asks a group of ship mice, the bravest of their kind, for help, but when they find out that the villain behind this event is the terrifying weasel-leader Noroi, they give up on helping Chuta. However seeing the hopeless Chuta, Gamba promises him to save the island, his family and the other mice. Gamba and his friends team up to go on their adventure to defeat the evil Noroi and his clan.