When Susan and Peter's cruel and selfish aunt decides to put them in a children's home, they decide to run away and set up home in the huge hollow trunk of an enormous tree that they have discovered in the heart of a large wood. With the help of their friend Angela, they furnish their new home and begin to enjoy life away from their cruel aunt. However, things start to go wrong. Angela disappears and the children spot a policeman and search party in the distance...