Anna Holm Ingrid Bergman is an embittered woman with a facial disfigurement that distorts her eye and mouth on one side and scars her cheek. She has expressed her alienation from society by joining a criminal gang that specializes in blackmail. This gang has two notable operations at the film’s start: they are demanding a large sum from a doctor’s wife, Mrs. Wegert Karin Kavli, for letters she wrote to a lover, and they are pressuring Torsten Barring Georg Rydeberg, a wealthy Consul’s dissolute nephew, who is entangled in their complex schemes and owes them increasing sums, to murder the little boy, the Consul Magnus Barring’s orphan grandson Lars-Erik Barring Göran Bernhard, who stands between him and inheriting the Consul’s estate.
To succeed in this, the gang needs a woman accomplice to be sent as the little boy’s governess and help kill him; they deplore the fact that Anna’s face makes her ineligible for this.
Anna goes to Dr. Allan Wegert's house to threaten Mrs. Wegert into paying for the letters; Mrs. Wegert gives her all her jewellery, which she puts in her purse, but it is only half the sum the gang demands. Dr. Wegert comes home, and Anna injures her foot trying to escape through the window. Dr. Wegert finds the jewellery in Anna's purse and, not suspecting she is a blackmailer, takes her for a burglar, but is interested in the problem of her disfigured face. He is a plastic surgeon who has specialized in restoring the faces of men damaged in World War I.
Instead of turning her in, he puts her in his hospital, heals her foot, and operates on her face. Mrs. Wegert goes to the hospital to see if Anna will give to her the letters if the surgery is successful. As Anna is taken to Dr. Wegert for removal of the bandages, she gives to Mrs. Wegert the letters, asking for nothing in return. The operation is successful, and Anna is beautiful; she is also moved by her talks with Dr. Wegert to become a different person.
Anna is now fit to go north to Forsa, where the Consul's estate is situated, as governess to his grandson, Lars-Erik, under a new name, Anna Paulsson. Already conflicted about helping Torsten murder the boy, she turns against the idea entirely as she grows to love Lars-Erik and the warm family atmosphere surrounding him. A close friend and employee of the family business, Harald Berg [Gunnar Sjöberg], is treated like a member of the family (Lars-Erik even calls him uncle), and he falls in love with Anna, who begins to reciprocate.
The head of Anna’s gang and the other members turn up at the hotel in town to urge her to get on with the plan, and Torsten presses her to proceed. On a winter night sleigh ride, Torsten manages to be in a sleigh alone with Lars-Erik and whip the horses into running off with it, while Anna, in a sleigh with Harald, realises that he means to fake an accident that kills Lars-Erik and desperately motivates their own pursuit. As the two sleighs race through the snow, Anna confesses the murder plot to Harald, and they manage to catch up. She snatches Lars-Erik from Torsten’s sleigh, but Harald is thrown from their sleigh and badly injured. Torsten drops his torch on the snow and rides off into the darkness. The gang members, hearing what has happened, good-naturedly give up on Anna and leave town.
In the aftermath, Anna remains with the Barring family as governess, and Harald begins to recover. The Consul reveals that Harald has resigned from the firm and plans to travel, hoping Anna can persuade him to return. Anna visits Harald in Dr. Wegert’s clinic and tells him her life story, including how as a child her face was burned in a house fire and she was abandoned by criminals who raised her to crime. She concludes that her ugliness, paradoxically, has kept her from becoming worse. Harald is torn but deeply in love, and he proposes that they go away and start a new life somewhere else. She declines for his sake, and he returns north to Forsa to rejoin the family.
Dr. Wegert, whose marriage has broken up without help from the gang, decides to leave Sweden with the Red Cross to China. He invites Anna to accompany him as a governess to his cousin's child in Beijing, and she gratefully agrees. They sail off together, with a shared vow to forget the past and begin anew.
