Geronimo Stilton and his family save a young dinosaur from the river. The dinosaur and Benjamin quickly become good friends. But it turns out that the dino has tremendous talent for mischief! Can Geronimo get him back to his herd before he causes a megalithic disaster?

Geronimo Stilton is a best-selling children's book series published by Edizioni Piemme of Milan, Italy, since 2000. Scholastic Corporationhas published the English version of the series since February 2004. Although the series credits its title character as the author, the idea was originally thought of by Elisabetta Dami. On older novels, the copyright is issued to a pseudonym "Geronimo Stilton"; this was changed on newer books. The books are intended for readers in the 6–12-year-old age range.