The Underwater Planet (Geronimo Stilton: Spacemice Series #6)

While at the beach, Geronimo Stiltonix stumbles upon a mysterious treasure map! The spacemice follow it and end up on Aquarix, a planet that's entirely underwater. During their exploration, they face fur-eating seaweed, ferocious piranha aliens, and . . . pirate spacecats! Squeak! Can the spacemice keep the spacecats from stealing the treasure?