Labbé, a hatter in a French provincial town, leads the life of a respectable citizen but is in fact a serial murderer. The only person to suspect this is his neighbour Kachoudas, an Armenian tailor. After the hatter kills his own wife, he then kills six of her friends to stop them visiting her and prepares to murder a seventh when the intended victim dies naturally. As a substitute, he murders the maid. At the same time, Kachoudas is dying and Labbé confesses his crime to him. Then, after getting drunk he visits his favourite prostitute Berthe and kills her too, being found there in the morning by the police.