The Lost Treasure of the Knights Templar

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.

The snake crown is stolen (or taken back) from the Knight Templars by the earth worshippers of Crete; the three kids try to retrieve it on behalf of the Knight Templars.

14 y.o. girl's dad is kidnapped by men, who are interested in the Knights Templar treasure. With 3 friends she sails from Bornholm, Denmark, to Gotland, Sweden, to free her dad and perhaps even find the treasure.