Rumini, a curious and daring young mouse, sails the seas as a cabin boy aboard the Wind Queen. Captain Bojtos Benedek and his crew have already shared countless adventures, and Rumini, together with his best friend Balikó, always seems to find himself wherever something unusual is about to happen.

This time, the Wind Queen is heading towards Mouse City when, during a brief stop, Sajtos Rozi is stung by a mercury hydra. The venom slowly begins to turn her body into silver, and only one antidote can save her – a remedy found on the mysterious Mirror Island.

With every minute counting, Rumini, Balikó and Galléros Fecó decide to take matters into their own hands. In the strange world of Mirror Island, they encounter dragons, the mysterious creatures known as foncsors, and the enigmatic Lady Vanita, while countless dangers await them along the way. Once again, they will need all their courage and resourcefulness to uncover the island’s secret and find the antidote before it is too late.