When Nurse Keate arrives at the Thatcher estate to care for a man with a bullet in his shoulder, she's told that he shot himself accidentally-but when the convalescing man is murdered soon thereafter, it becomes clear that the only "accident" was his not being fully killed the first time around. A murderer stalks the manor and yet the rest of the family isn't the slightest bit alarmed; instead, they seem intent on concealing the crime and adding it to the other dark secrets buried deep within their mansion's walls. Meanwhile, Nurse Keate is passed from one family member to another, each one claiming some spurious ailment requiring her expertise, realizing only too late that the family is anxious to keep her and her knowledge of the crime from leaving the premises. After another apparent murder takes place, she begins to fear that the price of this knowledge may be her life.