Geronimo Stilton #1: Lost Treasure of the Emerald Eye Book

Geronimo Stilton, editor-in-chief of The Rodent's Gazette, and author of numerous books featuring exciting stories that are tastier than Swiss cheese, is pulled into a mystery, when his sister, Thea, discovers an old, mysterious map that shows a faraway island, where there is a secret treasure hidden. Being the adventurer that Thea is, she decides to go to the island and find the secret treasure. Of course, she demands that not only Geronimo accompany her on her trip, but also their cousin Trap. Now the three of them are on an adventure that they will never forget.