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Legendary cinematographer (Freddie Francis) directed this Hammer horror film of madness and murder. The story concerns young Janet (Jennie Linden), a student at finishing school who is suffering from a series of recurring nightmares, having witnessed her mother stabbing her father to death. When her nightmares intensify, Janet is brought to the home of her guardian, Henry Baxter (David Knight). Henry is not home, but Janet is put into the care of his live-in nurse, Grace (Moira Redmond). Janet's nightmares continue, in which she sees a woman in white beckoning her into her parents' bedroom. Following the apparition, Janet sees the woman lying in bed, with a knife sticking from her chest. When Henry returns home, he is told by the doctors that Janet should be confined to a mental institution. Henry refuses, but the arrival of Henry's wife changes all that -- when Janet sees Henry's wife, who resembles the woman from her dreams, she grabs a knife and stabs her to death. Janet is committed to an institution for the criminally insane. However, it turns out that Grace had deliberately disguised herself as the woman in white to drive Janet over the brink and kill Henry's wife, so that they could be married. Henry and Grace get married, but Grace then receives reports that Janet has escaped from the institution and is returning to Henry's estate, bent on revenge.