This is a story about two sisters called Jean and Bridget Ferguson, who live with their mother Nina outside Cambridge. Their father passed away some years ago from a heart attack. A letter from an aunt, who lived on a Caribbean Island had invited the girls for their holidays. The letter was addressed to Jean, who had never heard of an aunt living so far away. They decide to go on this adventure hoping to have a great time. During their stay with this aunt, they go sailing to many islands. However, a storm blows up and they have to shelter in a large cave beside a cliff. Somehow Jean gets separated from the other passengers, and turns up on another island, where the notorious pirate lives. Will she be rescued.