6, The Underwater PlanetBook - 2016
When you're with Geronimo Stilton,
Geronimo Stiltonix accidentally comes into possession of a mysterious treasure map! The spacemice follow it and end up on a strange underwater planet. During their exploration, they face giant kelp forests, ferocious piranha aliens, and ultimately... pirate spacecats! Squeak! Can the spacemice keep the spacecats from stealing the treasure?