Mrs. Stevenson is an "invalid" who is bed-ridden due to an unspecified illness or condition. For the duration of the radio play, Mrs. Stevenson repeatedly (and unsuccessfully) tries to reach her husband on the phone because she is worried about her safety. Mrs. Stevenson is typically attended by a nurse, but we learn, through the protagonist's conversations with the telephone operator, that she has given her nurse the night off.
Throughout the course of the radio play, Mrs. Stevenson grows more and more agitated, demanding, and panicked. She is afraid to be home alone, since the patrol officer on her block has left, and her calls to the police (they don't seem to be worried for her safety) and then to a hospital (she wants to hire a nurse for the night) are unsuccessful.
We learn, at the end of the play, that Mrs. Stevenson's fears were justified. However, many audiences don't feel much sympathy for her because of her behavior. (Many readers/audiences describe her as rude and/or annoying.) Ultimately, much of the way audiences feel about Mrs. Stevenson depends on the actress who plays her.
The film was adapted by Lucille Fletcher from her radio play. Stanwyck plays Leona Stevenson, a spoiled, bedridden daughter of a millionaire. The telephone is her sole connection with the outside world. One day, while listening to what seems to be a crossed phone connection, she eavesdrops on two men planning a woman's murder. Leona calls the phone company and police, only to be ignored. Adding to Leona's dilemma is the fact that her husband Henry (Lancaster) is missing.
After a number of phone calls, the terrorized Leona begins to piece together the mystery. Her uneducated husband, who works for her wealthy father, turns out to be not all he seems. She finally realizes that she is the intended victim.