All Paris is frightened by the murders attributed to "Bluebeard". Modiste Lucille is introduced to Gaston Morrell, a puppeteer and painter, by a friend. They are drawn to each other, and she accepts a commission to design costumes for his puppets. Their budding connection adds a glimmer of warmth to a city on edge, and Lucille hopes art and affection might steer Morrell away from darker impulses.
At home, Morrell is confronted by a jealous Renee, who performs in Morrell's puppet show and is his lover. When she wonders what became of the models who had posed for him, he strangles her and dumps her body in the Seine River. The shocking act marks the first deadly consequence of Morrell’s complex psyche, and Parisian whispers begin to circle around the painter who can conjure beauty on canvas and horror in life.
Art dealer Jean Lamarte is aware of Morrell's homicidal tendencies, but keeps his secret as Morrell's paintings fetch high prices. Yet, when he sells Morrell's latest work to a Duke of Carineaux, he overestimates his own safety. The duke displays the collection, and a guard on duty recognizes the portrait as one of Bluebeard's victims, pulling Lamarte deeper into a fatal game of greed and exposure.
Inspector Lefevre of the Sûreté calls in one of his best undercover agents, Francine, who happens to be Lucille's sister. She and her "father" go to Lamarte to have her portrait done. Lamarte is on his guard, but her father is willing to pay a very large commission to find the man responsible for the duke's painting, and Lamarte's greed overcomes his caution. The plot thickens as the art world collides with law enforcement in a dance of deception and danger, drawing the siblings of Lucille closer to the truth.
Morrell has decided to give up painting (which triggers his murderous compulsion) out of love for Lucille, but Lamarte pressures him into one last picture to make him financially independent. However, [Francine] recognizes him, having met him briefly earlier at her sister's apartment, and Morrell has no choice but to dispose of her. Certain that Francine and her father were working for the police, Lamarte tries to flee, but Morrell catches him and kills him too, before escaping. The only clue he leaves behind is the cravat he used to strangle Francine.
At Francine's funeral, Inspector Lefevre shows Lucille the cravat. She knows it belongs to Morrell, as she had mended it for him. When she confronts Morrell, he tells her the story behind his crimes. As a starving art student, he had nursed back to health a woman who had fainted, fallen in love with her, and painted her portrait. She left without warning. When his painting was chosen to hang in the Louvre, he searched for her to tell the news, only to discover that she was a prostitute. Enraged by her contemptuous response, he strangled her. But ever since then, every model he painted turned into her in his mind, and he was compelled to kill her again and again. When Lucille tells him she is going to the authorities, he starts strangling her too, but the police break in. Lefevre saw that Lucille recognized the cravat and had her followed. After a rooftop chase across the city, Morrell falls to his death into the Seine.
