Four children dream of escaping the tedium of a summer holiday with their mother. When finally given permission to camp on their own on an island in the middle of a vast lake, they are overjoyed. But when they get there they discover they may not be alone… The battle for ownership of a lonely island teaches them the skills of survival, the value of friendship and the importance of holding your nerve.

On holiday with their mother in the Lake District in 1929 four children are allowed to sail over to the nearby island in their boat Swallow and set up camp for a few days. They soon realise this has been the territory of two other girls who sail the Amazon, and the scene is set for serious rivalry.