Geronimo's sister Thea is the mystery-loving rodent, not him. But somehow Geronimo finds himself going undercover to get to the bottom of a case. Full color. Enter the world of Geronimo Stilton, where another funny adventure is always right around the corner. Each book is a fast-paced adventure with lively art and a unique format kids 7-10 will love. Slimy Swiss balls -- I hardly knew where to start. Geronimo Stilton, Secret Agent Mouse? Maybe I could get used to that.