The Mysterious Eye of the Dragon

When you're with Geronimo Stilton, it's always a fabumouse adventure! My sister Thea and my cousin Trap were not getting along! When grandfather found them arguing over who would get to join me on a trip to Brazil, he forced us all to go together. My friend Isabela needed my help finding a mysterious emerald. Could Trap and Thea stop shouting their snouts off long enough to help find the stone?