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! Can the spacemice keep the spacecats from stealing the treasure?

When Space mouse Geronimo Stiltonix helps an alien spacecraft get back to its home planet, their queen becomes enchanted by Geronimo, and tries to force him to marry her and stay on the planet Flurkon forever.

"Professor Greenfur, the onboard scientist on spaceship MouseStar 1, has changed color from green to--orange! What's going on? To find out, the spacemice travel to his home planet of Photosyntheson. There, they learn that all of Professor Greenfur's relatives are being threatened by the nibblix, tiny aliens with very sharp teeth! Can the spacemice help in time?" --

Geronimo Stiltonix and the spacemice are visiting a planet where the most delicious wild mozzarella grows. Yum! But there's an attack of the slurp monster -- a scary alien who also loves mozzarella! Can the spacemice restore harmony between the monster and the other aliens of the planet without getting slurped up themselves?