In the small town of Caulfield, Helen Ferguson reflects on her loving marriage and comfortable home, which have been disrupted by a murder. When she learns that the police are on their way to her house, Helen prays that her sins will not be visited on her son, and recalls the events that brought her to this point: Years before, in New York, Helen's boyfriend, Stephen Morley, cruelly dumps her because she is pregnant. Although she is destitute and homeless, Morley refuses to see her when she comes to his apartment, and merely slips a train ticket for San Francisco under his door. On the train to San Francisco, Patrice Harkness, who is also pregnant, and her husband Hugh take pity on Helen and offer her one of their seats. Patrice and Helen become friendly, and Helen learns that Patrice is on her way to meet her in-laws, who are planning to help support her and Hugh during her pregnancy. While they are in the washroom, Patrice gives Helen her wedding ring to hold. Just then, the train crashes, and Helen is knocked unconscious, while Patrice is killed. After her baby boy is delivered by caesarian section in the hospital, Helen awakens and discovers that she has been mistaken for Patrice, whose ring she still wears. Although Helen tries to tell the doctor the truth, he believes that she has become hysterical because of the news of Hugh's death and sedates her. As Patrice had no family, and the Harkness family is now caring for her, Helen decides to maintain the pretense for the well-being of her baby. After her full recovery, Helen travels to Caulfield, where she moves in with Hugh's parents, and meets Hugh's brother Bill. Helen is tormented by her deception, but nevertheless allows her child to be baptized as Hugh and settles comfortably into the Harkness home. The Harknesses attribute Helen's lack of intimate knowledge about Hugh to the accident. Bill, however, becomes convinced that Helen is an impostor, but because he has fallen in love with her, he does not reveal his doubts. By Christmas, the Harknesses have changed their will to favor Helen and her son, although Helen vehemently asks them not to. Bill confesses his love to Helen, but she asks him for more time. One night at a country club dance, Helen is shocked to see Morley, who later demands money to keep quiet and threatens to take baby Hugh. Mrs. Harkness opens a bank account for Helen, and she uses the money to pay off Morley. Rather than leave town as he had promised, however, Morley then demands that Helen marry him, so that he will share her inheritance when the elderly Harknesses die. As the Harknesses dote on Helen, she buckles under the pressure. At the last minute, however, Helen refuses to proceed with the marriage, and Morley telephones the Harknesses. Mrs. Harkness, who has a weak heart, answers the phone and hears only Helen's voice in the background pleading with Morley. Helen reluctantly marries Morley, but Mrs. Harkness is alarmed and tells Bill about the mysterious phone call. When Helen gets home, she takes Mr. Harkness' gun and goes to Morley's office, intending to kill him. Although she finds that Morley is already dead, Helen fires a shot just to be sure. Bill, who has followed her there, believes that she has killed Morley, and helps her remove the evidence, then dumps Morley's body on top of a passing freight train. On the drive home, Bill admits that he always knew she was not the real Patrice, but is unswerving in his love for her, and Helen confesses she cares for him. When they get home, they find that Mrs. Harkness has died of a heart attack, and Helen blames herself. Three months later, Helen and Bill are married, and the Harkness family maid, Josie, brings Helen a note that she had been holding in the event of an emergency, in which Mrs. Harkness claims responsibility for Morley's murder. Although neither Bill nor Helen believe that she was the killer, Bill insists on giving the note to the police in order to clear his wife. When the police arrive, Helen admits the truth, but the police reveal that Morley's killer, his girl friend, was captured during a gambling raid and made a full confession. Bill and Helen are at last free of the shadow of guilt that oppressed them.