Late on a hot Dublin night, Dr. Margaret Mitchell, a widow in her mid-forties, phones the police with a sense of dread and foreboding. Her daughter, Mary, went out with some friends twenty-four hours ago. She has not come home. Two days later, Margaret receives an anonymous phone call. Having worked in an institution for the criminally insane, Margaret is all too familiar with what she hears on the other end of the line and it fills her with terror.

A week later an old man walking his dog beside a canal finds the body of Mary Mitchell half-submerged in the water. She has been raped, tortured, and beaten to death. Inspector Michael McLoughlin, who has a reputation as a drinker and a womanizer, is assigned to the case. Although he was once a successful detective, there are now doubts about his stability. McLoughlin is taken with Margaret's beauty and the force of her personality: he becomes obsessed and watches her constantly.

The killer, meanwhile, has transferred his desire to damage and kill to Margaret, who finds herself drawn to the man who ruined her life and destroyed her daughter's.