Gaston Morel, a puppeteer, falls in love with Lucille, a young modiste, and confesses to her to be a murderer. His story and his first murder are told in flashback. Morel was once a painter and fell in love with a model who became the main inspiration for his paintings, but when she betrayed the idealized image he had of her, he killed her. She is just the first victim of a long series of murders, including Lucille's sister.