On a summer night in 1829, an old mansion on the coast of Cornwall froze, listening to the last breath of the hostess - Lady Treverton - who left the mortal world and left her inconsolable husband, her little daughter Rosamond and many questions unanswered.

What did she hide from everyone until her death, and what did she manage to confess only on her deathbed, dictating a message to her maid Sarah Leeson? Why does Sarah not find the courage to take the letter to her master, but hides it in one of the abandoned rooms and immediately leaves the house? And why, sixteen years later, is she trying to prevent Rosamond from returning to her childhood home and entering the room?