The Spiral Staircase (1975)

A serial killer has been terrorizing a community, his five victims thus far being young women all with some form of disability. Lieutenant Fields, leading the case, wants to show that he is keeping the community safe by his reckless actions. Within a certain circle, the focus moves to the Sherman mansion owned by Dr. Joe Sherman, the mansion, the family home, out of which he operates the Sherman Institute, an educational organization. That focus is because Helen Mallory, Joe her paternal uncle, has been "vacationing" there, it a euphemism for recuperating as she became mute due to a mental break in having watched her husband and her adolescent daughter die in a house fire, and as she is the girlfriend of Dr. Rawley, the Sherman family doctor and the medical examiner. Dr. Rawley and many in the family fear for Helen's life as a potential next victim. What may happen with Helen is as much at the hands of the serial killer as it is with the interactions of the disparate group at the mansion: Helen's wheelchair-bound diabetic paternal grandmother, the family matriarch; Mrs. Sherman's acerbic tongued nurse; Blanche, who is more to Joe than just his secretary; the household servants Mr. and Mrs. Oates, the latter who believes it's her right to pilfer whatever she wants out of the liquor cabinet; and recent arrival Steven Sherman, Joe's younger brother, a ladies man and war veteran, the brothers who have a classic sibling rivalry.