When, in the process of testing his newest time machine, Professor von Volt accidently brings a triceratops, Helen of Troy, Attila the Hun, Charlemagne, and Christopher Columbus to present day New Mouse City, it is up to Geronimo and his friends to return them all to their own times and places--without being eaten by a T-Rex or skewered by Trojan warriors.

Geronimo Stilton travels back in time to the ice age, ancient Greece, and Renaissance Italy. He encounters woolly mammoths, writes and stars in a play, and even helps put a bad guy in prison! But when the portal started malfunctioning, will Stilton and his family be able to get back to the present day, or would they get lost in time?