Geronimo Stilton is back with a new adventure. This time it is out of this world. New Mouse City is in danger. An evil professor starts threatening the city and its residents with all his terrifying and dangerous inventions. The authorities need help to thwart the evil professor’s intentions. They ask Geronimo Stilton to help by going on a top secret mission.

A mission like no other: Geronimo is to go on a top secret mission to the outer space. Though he was totally unprepared to go, there was no way to turn down the authorities when his home New Mouse City is in danger.