Journalist mouse Geronimo Stilton travels to New York to spend the Christmas holidays with his family and finds himself scurrying all over the Big Apple searching for his luggage, which has gotten mixed up with another mouse's.
After receiving a mysterious message summoning him to a meeting, Geronimo Stilton finds himself back in the Kingdom of Fantasy, summoned by the Elves, who want him to travel to the Great Explanatorium to find an answer to the earthquakes that are threatening the Kingdom.
Princess Sterling sends the Dragon of the Rainbow and Scribblehopper to bring Geronimo Stilton back the the Kingdom of Fantasy, because he is the hero in the dragon prophecy who will find the stolen dragon egg and restore harmony to the kingdom.