Dr. Margaret Mitchell, a widow in her mid-forties, having returned to Ireland from New Zealand after 20 years to nurse her dying mother, phones the police with a sense of dread and foreboding. Her daughter, Mary, had gone out with some friends 24 hours ago. She has not come home.Two days later, Margaret receives the first anonymous phone call. Margaret is a psychiatrist who has worked in an institution for the criminally insane. She understands what she is hearing and is filled with terror.