The Lost Treasure of the Knights Templar (2006)

Danish brilliant pre-teen student Nis uses his summer holiday to learn Latin so he can properly study the Knights Templar inheritance on Bjornholm island from sources. His friends Mathias, a dumb jock, and Kathrine, who only comes to spend time wear her dad, who really wanted a boy, prefer childish fun, but get dragged in his quest for a treasure. Mats's strength, Kathrine's connections and even Nis's bratty kid sister's blunt remarks contribute to find out about two brotherhoods, heirs of 12th century factions in the Templar order and deal with danger.