Three children find a treasure map in their Grandpa's shed and he tells them the story of how he came by it. It was from a time when he was a boy in the early 1960s. The story follows the adventures of seven children who are together over the summer holidays on a farm. While out fishing their boat is blown ashore onto a "forbidden island". They meet a fascinating old man on the island who claims to be a survivor from an ancient civilisation...