A 19th-century Parisian puppeteer is killing the young women he employs.

In nineteenth century Paris, the citizens are warned that a "Bluebeard," a strangler who preys on women, is at large. Lucille, a modest seamstress, disregards the warning, however, and while walking down the street one night with her friends Constance and Babette, she encounters puppeteer Gaston Morrell. When Lucille praises his skill, Gaston offers to stage a show for her and her friends the following evening. After the performance, Gaston invites Lucille backstage and, seeing how fascinated she is by his puppets, asks her to sew some new costumes for them. When Gaston explains that he fashions his puppets from people he knows and that the figure of Marguerite was modeled after a friend who met a tragic death, Lucille tries to cheer him up by inspiring him to create a new puppet and Gaston offers to design a figure in Lucille's image. Upon returning home that night, Gaston is reproached by Renee, a puppeteer in his show, who jealousy upbraids him for his faithlessness. When Renee questions Gaston about the mysterious disappearance of the women with whom he has dallied, he pulls off a cravat from around his neck, strangles her and dumps her body in the Seine. The next day, Inspector Lefevre of the Paris police summons Gaston to identify Renee's body. After leaving the police station, Gaston orders Le Soldat, his assistant, to escort Lucille to his studio. There, Lucille finds Gaston's torn cravat and mends it for him. After she leaves, art dealer Jean Lamarte comes to inform Gaston, who secretly paints women's portraits, that he has sold the puppeteer's newest portrait . Lamarte, who knows that Gaston is driven to murder his models, and usually sends his portraits out of the country and away from the eyes of the authorities, confesses that he sold this last painting to a duke who resides in Paris. When the duke decides to exhibit his collection, Lefevre attends the exhibition and recognizes the woman in the portrait as the latest murder victim. Told by the duke that he purchased the painting from Lamarte, Lefevre questions the art dealer, who claims he bought the work from an old man whose name he does not know. Soon after, Lucille's younger sister, Francine, an operative in the French police force, returns home from abroad, and as she dresses behind a screen, Gaston delivers a bouquet of flowers and a puppet to Lucille. After he leaves, Lefevre, Francine's superior, visits and when Francine learns about the strangler, she proposes that she pose as the daughter of a wealthy South American businessman and commission a portrait from the artist. Posing as her father, Inspector Renard approaches Lamarte about hiring the artist of the duke's paining to render a portrait of his daughter. When Lamarte offers Gaston a large sum of money to paint the portrait, the artist, who is in debt to Lamarte, agrees on condition he can use the studio above Lamarte's shop. After Lamarte contacts Renard, the police plan a trap in which the lighting of Renard's cigar will signal the waiting officers to enter the shop. When Renard and Francine arrive at the shop, Lamarte instructs Renard to remain downstairs while he escorts Francine upstairs to the artist's studio. Nervous about revealing his identity, Gaston paints from behind a sheet, tracing Francine's reflection from a mirror. Upon returning to his office below, Lamarte becomes suspicious of Renard's pacing in front of the window and draws the curtain. Upstairs, meanwhile, Francine, determined to uncover the artist's identity, insists that he pose her, and when he steps from behind the sheet, she recognizes Gaston and accuses him of murder. When he loosens his cravat and starts to strangle her, her screams alert Renard, who tries to signal for reinforcements but is knocked unconscious with a candlestick by Lamarte. Thinking that Lamarte has betrayed him, Gaston strangles him with his bare hands, just as the police, impatient for the signal, break down the door. Gaston escapes through a hidden passage and later reappears at Francine's funeral, where he offers Lucille his condolences. Noticing the unusual material of Gaston's cravat, Lucille follows him back to his studio and asks to see the cravat that she had previously mended. When Lucille demands to know why Gaston had refused to paint her, he confesses that he is in love with her and discloses his tormented history as a struggling artist: Finding an unconscious girl prostrate on the street one day, Gaston took her home, nursed her back to health and began to paint her portrait. After Gaston finished the painting and delivered it to Lamarte, his model, Jeanette, deserted him. When the painting was awarded the honor of hanging in the Louvre, Gaston searched for Jeanette to tell her the good news. Upon discovering that she has embarked upon a tawdry and debased life, Gaston, repulsed, strangled her, and from then on, he saw Jeanette in all his models and strangled them. Unable to forgive Gaston for murdering her sister, Lucille threatens to go to the police and he attacks her. Just then, Lefevre, who has followed Lucille, breaks down the door, and Gaston flees to the roof. As the police pursue him across the rooftops, Gaston slips and falls to his death in the Seine.