Louise (Danielle Darrieux) is an aristocratic woman of Belle Ãpoque Paris, married to AndrÃ© (Charles Boyer), both a count and a high-ranking French army general. Louise is a beautiful, but spoiled and superficial, woman who has amassed debts due to her lifestyle. She arranges to secretly sell her costly heart-shaped diamond earrings, a wedding present from her husband, to the original jeweler, Mr RÃ©my (Jean Debucourt). Relations between Louise and AndrÃ© are companionable, but they sleep in separate beds, have no children, and AndrÃ© has a secret mistress, of whom he has recently tired. Louise disguises the disappearance of the earrings by pretending to have lost them at the opera. The search for them eventually reaches the newspapers ("Theft at the Theatre") which in turn prompts RÃ©my to go to AndrÃ© and "discreetly" offer to sell them back. He accepts cheerfully and, rather than confront his wife, coolly gifts the earrings to his mistress, Lola (Lia Di Leo), whom he happens to be seeing off permanently to Constantinople.
At her destination, however, Lola soon sells the earrings herself to settle gambling debts and they are later purchased by an Italian baron, Fabrizio Donati (Vittorio De Sica), who is on his way to a high diplomatic post in Paris. Through a series of encounters, Donati becomes infatuated with Louise, later dancing with her long into the night at a ball. AndrÃ©'s long absence "on maneuvers" facilitates the couple's affair. With each passage of time, the Baron asks Louise if she has heard from her husband. AndrÃ©'s return prompts Louise to stop seeing Donati, but during a hunting excursion where all three are present, she witnesses Donati fall from his horse and faints. She is said to have a "weak heart," but AndrÃ© sees this behavior as an affectation, and the event makes him suspicious.
Louise becomes disconsolate and announces that she will take a long holiday in the Italian Lake region, alarming both her husband and her lover. Donati brings gifts: roses with the very earrings she had sold earlier. What she had cast aside so easily before suddenly has real meaning to her. On her own in Italy, Louise tries to forget Donati who regales her with letters, to which she writes responses, all of which she promptly destroys. She ends up meeting with him secretly again and confesses that she's able to console herself only through possession of the earrings, which she now identifies with her lover, not her marriage. Upon her return to Paris, Louise resolves to continue with the affair. To explain the reappearance of the earrings, she now creates an elaborate ruse that they had been misplaced in one of her gloves the entire time, making a big show of "finding" them in front of AndrÃ©. He knows she is lying but says nothing.
At yet another formal ball, AndrÃ© takes the earrings from Louise, quietly takes Donati aside, and confronts him about them, revealing their true history. He then gives them to Donati instructing him to sell them back to the jeweler, so that he may buy them back a third time to give yet again to Louise. Before departing, Donati informs Louise he can no longer see her and expresses his pain at learning of her lies. Louise falls into a deep depression. AndrÃ© presents her with the earrings he has bought back and informs her that her unhappiness is her own fault and that she must give the earrings away to his niece who has just given birth. Louise tearfully agrees. The niece is soon forced to sell the earrings yet again to RÃ©my to pay off her own husband's debts, and RÃ©my offers to sell them back to AndrÃ© for a fourth time, but he now angrily refuses. Louise goes to the jeweler herself and buys the earrings back with money from sales of her other jewelry and furs. She informs AndrÃ© of what she has done. In his anguish at having lost her love â or perhaps never having had it â AndrÃ© goes to the gentleman's club where he confronts Donati on the pretext of a slight and challenges him to a pistol duel.
Louise pleads with Donati not to go through with the duel; AndrÃ© has been seen to be an excellent shot and will surely kill him. Donati is pensive, but refuses to back out and arrives at the dueling field with his and AndrÃ©'s seconds. Meanwhile, Louise goes to the Church of Saint-Ãtienne-du-Mont to pray fervently at the shrine of St. GeneviÃ¨ve that Donati be spared â the same place where she was seen earlier praying frivolously that the jeweler will be willing to buy back her earrings. She then races with her servant to the duel just as the agents inform the duelists that the "offended party," AndrÃ©, is allowed to fire first. He takes aim at Donati, who stands unflinching. As Louise hastens up the hill toward the duel, a single shot is heard, but no second shot, implying that one duelist may be dead. She slumps against a tree as the servant runs off for help.
Ultimately it is seen that Louise has left a burning candle at the shrine, along with her prized earrings, and a card reading that they are a gift from her.
Who refuses to back out of the duel?
Donati