She was portrayed by Shelley Winters.
The movie opens with a Hearst Metrotone newsreel from the 1930s telling of the Iowa murder of Ellie Banner by Leonard Hill and Wesley Bruckner. As they are seen being loaded into a paddywagon following life sentences in prison, the focus shifts to their mothers, Helen Hill and Adelle Bruckner, as they fight a crowd to their car.
In the car, the grainy footage shifts to color, and Helen reveals that someone in the crowd cut the palm of her left hand. Soon at home and tending to her wound, Helen receives an anonymous phone call from a man, "I'm the one who cut you.... I wanted to see you bleed." This caller threatens to make the mothers pay for the sins of their sons. Helen and Adelle change their names, leave Iowa and head to Hollywood, where Adelle opens a dance academy for little girls who want to be the next Shirley Temple.
Soon after arriving, Hamilton Starr, an elocution teacher offers his services to Adelle's school, and she takes him up on his offer, much to Helen's chagrin, as Helen is frightened of the menacing man. Soon, the phone calls resume and Helen believes a strange man is watching their home. She has hallucinations, especially at a show where she think she sees Starr with a knife.
Adelle falls in love with Lincoln Palmer, the father of a student, and Helen grows jealous of the budding relationship. Helen takes solace in her faith, listening to a radio show hosted by evangelist Sister Alma.
Helen's jealousy of Adelle's romance with Lincoln leads to a fight, at which point, Adelle demands that Helen move out. Adelle then heads for her date with Linc. As Helen readies herself to move out, a mysterious intruder enters the house, walks up the staircase, and calls her real name. Helen reacts by pushing him down the stairs. When he lands at the bottom, his head is gashed open, blood seeping on the floor, and Helen envisions her late husband, who was mutilated by a plow, and the dead Ellie Banner.
Adelle arrives home to find the dead stranger, and, fearing publicity, decides to dispose of the body. As the rain pours, she and Helen drag the dead man into the street and dump him into an open hole adjacent to their home where crews had been doing construction. The body is discovered the next morning, and it is presumed the man fell into the hole to his death.
Helen's guilt builds and she visits to the church to see Sister Alma and atone for her sins. Sister Alma offers her forgiveness, but an irrational Helen makes a spectacle and is dragged away by Adelle. Off-screen, Helen sees a doctor and is ordered to bed rest.
Adelle goes to a miniature golf course with Linc, where he proposes. He drives her home to make preparations to elope that evening. Arriving home, Adelle notices that Helen is not in her room and follows a trail of blood out the back door and down to a rabbit cage, where she finds Helen's pet rabbits slaughtered. Helen steps out of the shadows and reveals that she killed them and pushed her husband off a plow to his death. Adelle leads Helen into the house and is phoning Sister Alma, when she lets it slip that she plans to wed Lincoln. Helen pulls a knife from her robe, stabbing Adelle in the back. As Adelle falls dead, the doorbell chimes.
Helen answers the door and finds a detective, who shows her a photo of the man she pushed down the staircase. When she claims not to recognize him, the detective reveals the man was Ellie Banner's boyfriend, who came to California with plans to murder the ladies.
Later, Lincoln arrives, expecting to whisk Adelle away. From the street, he can hear someone pounding, "Goody Goody" on the piano. He enters the house calling Adelle's name and follows the sounds of the piano up to the rehearsal hall. There, he finds Helen giddily playing the song and Adelle, dressed in her signature dance costume, tied to a ladder on stage. The music grows more and more frantic as Helen laughs, and the camera moves in for a final closeup.