Susan Mottram lives an idyllic existence until her eighteenth birthday, when her father's sudden death plunges the family into penury. To support her mother and younger sister, Susan takes employment as a teacher at a remote Yorkshire boarding school, Matterdale Hall, owned by the radical Dr. Claybourn and his penny-pinching wife. Susan soon discovers that all is not as it seems. Why is little Mary so silent? What really happened to Susan's predecessor? Is anyone safe in the school's draughty halls? Through a life-changing meeting with the beautiful and mysterious Cassandra, Susan begins to uncover the truth about Matterdale Hall, and discovers the cruelty, and love, that can lie within the human heart.