Tom discovers his next door neighbours are hiding a secret that's beyond his wildest imaginings. At the bottom of the Tuttle family's garden rises a huge hedge, as tall and as solid as the wall of a castle. Behind it live the Grimleys, but what they're trying to hide no one knows. Then one evening Tom Tuttle hears an eerie wailing. What sort of creature could make such a noise - a noise that stops when Tom's sisters sing? And if he uncovers the truth, will anyone believe him?