The story is about a family who are on holiday with their father in Scotland. This is the first time that their father has joined his three children on their summer holiday and they are staying, as they have before with their Grandparents who own a large highland estate.The children have friends who are the daughters of another estate owner on the other side of the Loch which they look out on. Witch Island is the mysterious dark island that lies between the two estates in the middle of the Loch and where the children have their summer adventures.