A con artist and his criminal cohorts hold an old lady hostage in her own home.

In December, in turn-of-the-century London, the wealthy and generous Mrs. Mary Herries shows her new banker, Mr. Foster, her magnificent art collection. That same day, an impoverished artist named Henry Springer Elcott comes to the door and admires her Benvenuto Cellini doorknocker. Soon after, Mrs. Herries talks with Elcott after seeing him painting a picture of her house. Elcott then comes to call bearing paintings, which he hopes she will buy. After admiring her beautiful things, he suddenly leaves, but does not take his paintings. A moment later, she notices that he has stolen an expensive cigarette case. A few days later, Elcott approaches her in a bookshop and returns the cigarette case, apologetically telling her that he pawned it, but redeemed it after selling a painting. He then convinces her to come to his flat, which he shares with his sweet, malnourished wife Ada and their baby, to see more paintings. At the flat, Mrs. Herries leaves abruptly when Elcott bristles at one of her comments, but she sends a check and a note instructing him to buy his wife warm clothing. Elcott then takes a portrait of Ada to Mrs. Herries, while Ada and the baby wait outside. When Ada faints, she is brought in by a passerby, who says he is a doctor and suggests that Ada may have pneumonia. The sympathetic Mrs. Herries takes Ada into her home, where she remains for two weeks. Mrs. Herries becomes increasingly suspicious of Elcott, but does not say anything because she has grown fond of Ada. Elcott, who secretly is in cohoots with the phony doctor, soon begins to behave as the master of the house, causing Dora, Mrs. Herries' cook, to quit abruptly. When Mr. and Mrs. Edwards, supposed friends of Ada, suddenly show up on the doorstep, Mrs. Herries has had enough and decides to move Ada to a nursing home and send the rest packing. When the Edwardses and Elcott menacingly enter Mrs. Herries' room, she orders them out, but Elcott demands money for all of his "work," and they tie her up and close the windows. Because Edwards overhears Mrs. Herries' faithful maid Rose calling the nursing home, he has his wife cancel the order and locks Rose in her room. On Christmas Eve, when the local constable comes for his promised gift, Elcott elicits the man's sympathies by saying that Mrs. Herries has become violently mentally ill. Soon Elcott begins to sell Mrs. Herries' fine antique furnishings, telling the buyers that she is ill and is moving to the country. Ada is now better, but concerned because the baby has been sent away. Elcott dismisses her concerns and orders her to care for Rose, who is still a prisoner. That afternoon, they bring Mrs. Herries downstairs to sign a power of attorney, but she refuses. When art dealer Monsieur Malaquaise comes by, she gives him a note, but Elcott had prepared the man with the insanity story. That same day, Rose's sister and brother-in-law, the Hartleys arrive, inquring about Rose's whereabouts. Elcott says that Rose left suddenly and implies a scandal, then offers them Rose's uncollected wages. Although Mrs. Harkley wants to call the police, her husband is satisfied with the money. Meanwhile, Mrs. Herries talks to Ada and concludes that she is a dupe. When Foster comes to call that afternoon, Elcott, who claims to be Mrs. Herries' nephew, is irritated when Foster says that in order to sell the house, the bank needs to examine Mrs. Herries personally. At just that moment Mrs. Herries starts down the stairs and Foster seems to conclude that she is indeed ill. Meanwhile, Mrs. Herries has convinced Mrs. Edwards, who has grown afraid of Elcott, that she can have money hidden in her room in exhange for a key. At the same time, Foster is talking to his superior at the bank and says that he wants to investigate Elcott. After giving Mrs. Herries the key, Mrs. Edwards tells her husband that they should leave immediately, but he refuses and strikes her when she protests. That night, a frightened Ada brings Mrs. Herries the portrait that Elcott had painted of her and reveals that her dead body has been painted into it. Ada then admits that in Paris, Elcott murdered another woman whose portrait he had painted. Mrs. Herries then gives Ada the key so that she can free Rose. A few moments later, Edwards sees the now freed Rose and kills her. Elcott is furious and, upon Mrs. Edwards' suggestion, concludes that Ada freed Rose. Just then, Foster telephones to say that he wants to see Mrs. Herries that night. Elcott decides that they must leave that night and goes to Mrs. Herries' room, where he finds the portrait. He then moves her in the wheelchair to which she has been tied and places her by the open window. Elcott lies to Edwards that Mrs. Herries knows that it was he who killed Rose. Elcott's plan is to have Mrs. Herries' "fall" occur at eight o'clock, when the constable is due to come by. At exactly eight, Edwards goes upstairs and throws the wheelchair-bound woman out the window. Elcott is pleased that Foster, too, has arrived at the propitious moment, but as they go to answer the door, Mrs. Herries and Ada appear in the drawing room. It is then revealed the women had placed Rose's body in the wheelchair after Ada warned Foster, who has come with the police. They take the Edwardses and Elcott away and Mrs. Herries says that she is all right now.