Eleven-year-old Elna sees two suspicious-looking individuals exchanging a shiny object, which could be a gold coin. With the help of three classmates, Karim, Jonathan and Pau, they will close ranks and begin a search that will be joined by a biochem...

Eleven-year-old Elna sees two suspicious-looking individuals exchanging a shiny object, which could be a gold coin. With the help of three classmates, Karim, Jonathan and Pau, they will close ranks and begin a search that will be joined by a biochemist grandmother and a young teacher with her dog. In their quest they will visit the Museum of Jewish History, a traditional pastry shop and other interesting places in the Old Quarter of Girona, following a clue that could lead to a treasure hidden many years ago. The problem is that a gang of unscrupulous evildoers seems to be pursuing the same goal...