Plot
Polish woman Viktoria Kowalska has lost her home and her husband in the German occupation of Poland and is imprisoned in the concentration camp at Belsen. She befriends another prisoner, Karin Dernakova, who dreams of reuniting with her young son Christopher, who was sent to live in San Francisco with a wealthy aunt.
Karin dies shortly before the camp can be liberated and Viktoria, seeing a way to a better life, uses Karin's papers to assume her identity. The camp is liberated by the Allies, and Viktoria is interviewed by Major Marc Bennett, who secures a place for her in a camp for people displaced by the war. She writes to Karin's aunt Sophia in San Francisco but receives a cable from lawyers that Sophia has died.
Four years later, Viktoria, still using the name Karin, travels to New York City, where she meets with Chris's guardian Alan Spender, Sophia's distant relative. Viktoria intends to gain custody of the real Karin's son, but it becomes clear that Sophia has left her fortune to Chris for when he comes of age. When she realizes that Alan is attracted to her, she decides that it will be easier to stay in the country if she has an American husband. She allows him to romance her, and they soon marry. Alan takes Karin to San Francisco, where Chris meets his the woman whom he believes to be his mother for the first time, and she settles into Sophia's Italianate mansion on Telegraph Hill, where Chris lives with Alan and his governess Margaret.
Things seem idyllic at first, but tensions mount between Karin and Margaret, who has raised Chris and is in love with Alan. Margaret resents Karin for intruding on her life. Karin is alarmed at the presence of a burned, dangerously damaged playhouse overlooking the hill, which Chris claims to have damaged with an explosion from his toy chemistry set. He and Margaret beg her not to tell Alan because Margaret never has, but Karin is perplexed to discover that he already knows about it. Karin is pleased to meet Marc again, learning that he is an old schoolmate of her husband and a partner for the law firm that handles Sophia's affairs. They are attracted to each other, but she keeps a respectful distance.
As Karin is investigating the playhouse, she is surprised by Alan and nearly falls to her death through a hole in the floor. Alan rescues her but is alarmed by her behavior. Soon after, the brakes on Karin's car fail on a day when Chris was supposed to be with her. She escapes unharmed but contacts Marc, telling him that she believes that Alan is behind the accident, as he will inherit Sophia's money if she and Chris were to die. With Marc's help, she begins to investigate the accident, but she cannot find conclusive proof. She reveals her true identity and Marc tells her that he is in love with her. When Alan states that his father might not have sent her the cable regarding Sophia's death, she grows significantly more nervous around him.
Karin discovers Sophia's newspaper obituary in Margaret's scrapbook confirming that the cable was sent three days before her death—proof that Alan must have sent it before he killed Sophia. Her attempt to phone Marc is thwarted when Alan arrives home, and he keeps his eye on her for the rest of the evening. When he brings her orange juice, she is sure that her glass has been poisoned. When he briefly leaves the room, she attempts to call the police but cannot, as Alan had left the phone off the hook in another room. He returns to the bedroom and coerces her into drinking the orange juice, and he then drinks his own. Believing that he is safe, he confesses that he murdered Sophia and that he has mixed an overdose of sedatives into her orange juice. Karin tells him that she has switched the glasses and that he has poisoned himself. She tries to telephone a doctor but cannot reach him. Margaret is awakened by the commotion and Alan begs her to phone a doctor. Realizing that he does not love her and he will never stop trying to kill Chris, Margaret watches as Alan dies.
Margaret is arrested for refusing to aid Alan, and Karin leaves the house with Marc and Chris to begin a new life.
