My sister, Thea, had discovered an enormouse old castle built by the founder of New Mouse City! She and Trap dragged me along with them to explore it. Inside, we found one hundred keys ... but only ninety-nine doors to unlock. What mysterious room did the hundredth key open? It was up to us to find it and reveal its secrets! BONUS! After the story, read an extra Mini Mystery adventure and jokes galore! About the Geronimo Stilton Series: Geronimo Stilton is not strong, he’s not bold, and he’s DEFINITELY not brave. Adventure?! What’s wrong with staying at home with a box of cheesy chews? Geronimo always seems to end up going on daring adventures, solving peculiar mysteries and entering tricky competitions. Will he ever get a relaxing break? The Geronimo Stilton series is perfect for 5-to-8-year-olds and reluctant readers due to its expressive typeset, fun illustrations and humorous stories.