On a summer night in 1829, an old manor house along the Cornish coast stood motionless, listening to the last breath of its mistress—Lady Treverton—who had left the mortal world, leaving her grieving husband, her little daughter Rosamond, and a host of unanswered questions. What did she hide from everyone until the very end, and what was she able to confess only on her deathbed—dictating a message to her maid, Sarah Lisson? Why doesn’t Sarah find the courage to deliver the letter to her master, and instead hides it away in one of the abandoned rooms, then immediately leaves the house? And why, sixteen years later, does she try to stop Rosamond from returning to her childhood home and entering the room?