In the vastness of space, a spaceship shaped like a slice of cheese speeds between galaxies, searching for new planets and bizarre aliens! It is the Top Galaxy, the spaceship of the Cosmonice Mice, the fearless space mice who travel the universe with their captain, the one and only Geronimo Stiltonix!

Geronimo stumbles upon a mysterious treasure map... Following it, the Cosmonice Mice reach the strange underwater planet Aquarix, where they encounter forests with dangerous seaweed, swarms of wild piranhax, and, finally, a group of... Cosmo Cat Pirates!

The brave Cosmonice Mice traverse space aboard the Top Galaxy, a mouse-tacular spaceship shaped like a slice of cheese. Here the crew has all the necessary amenities: ultra-luxurious cabins, restaurants, greenhouses for growing plants, libraries, theaters, amusement parks, gyms, sports fields, and even a biosphere that replicates various natural environments!