The Spiral Staircase
The events take place in a small New England town. An unknown murderer is killing young women with physical defects. Helen works for Mrs. Warren (Ethel Barrymore), a rich bad tempered old lady. Helen is mute, and is assumed to be a target for the murderer. Helen has been unable to speak since the trauma of seeing her parents burn to death in a house fire when she was a child.
Also in the house, are Mrs. Warren's two sons. Professor Warren is the "good son" who has cared for the mother and maintained the family mansion. Steve has travelled the world as a playboy, living off the family fortune.
Helen goes to the basement where she finds the body of another murder victim (Blanche, a young lady who had argued with Steve earlier). She screams and Steve shows up. Steve acts strangely, and Helen assumes he is the murderer. She manages to run by him, and lock him in the basement. Helen goes upstairs where she is confronted by Prof. Warren, who admits he is the killer. Prof. Warren tells Helen that both brothers felt despised by the father because they were weak and cowardly. He is killing these imperfect women to show he is tough and strong.
After a lengthy chase through the house, Prof. Warren has Helen trapped in the stairwell. Old Mrs Warren comes out of the room with a gun (which only Helen knew she had hidden in her room.) Mrs Warren knew one of her sons was the killer, but thought it was Steve. She shoots and kills Prof Warren, saving Helen. Helen screams, the new trauma has undone the effect of the old trauma, and she can speak again.