Geronimo receives a letter from his friend Isabela, who lives in Brazil. She asks him to help her find a huge emerald called "Dragon's Eye", discovered by her grandfather but which disappeared when he died. Neither one nor two, Geronimo embarks on the adventure, followed by his sister TÔea and his cousin Traquenard. Will the four friends succeed in deciphering the enigmas left by the grandfather, despite Geronimo's eternal clumsiness? And who is this mysterious young rodent who seems to be following them? From 8 years old.