In Paris, a relentless police force is determined to stop a serial killer who leaves a chilling calling card—Monsieur Durand—on every victim. The case lands with Wens, a cool, methodical inspector whose resolve is matched by his desire to see justice served. His personal life adds a complicated edge: his mistress, the glamorous but self-serving Mila Malou, Mila Malou, is chasing publicity as eagerly as she chases headlines, and she insists she’ll lend a hand in the hunt, even if her motives are as much about spotlight as about truth.
To crack the case, Wens zeroes in on a new clue: a petty thief produces a stack of Durand calling cards he found hidden in the attic of a boarding house at 21 Avenue Junot. Deciding to get closer, Wens adopts a disguise and moves into the building, presenting himself as a Protestant minister to blend in with the tenants and to observe from within. The boarding house becomes a microcosm of eccentricity and danger, a tense collage of characters who each hold a fragment of the truth. The residents include [Monsieur Colin], a craftsman who makes and sells unsettling Durand dolls with blank faces that seem to hint at hidden motives; [Dr. Linz], a former abortionist whose presence adds a layer of moral ambiguity; [Kid Robert], a blind former boxer whose past is as shadowy as the hallways he navigates; a self-styled 'Professor' Lalah-Poor, a fakir and stage magician who lifts pockets as easily as he lifts performances; another tenant who scribbles a mystery novel, while yet another daysdreamer obsessively studies different kinds of whistling. The air is thick with secrets, and every door seems to murmur with possibilities.
As the murders continue, Colin, Linz, and Lalah-Poor are arrested in sequence, yet each is freed when another Durand murder occurs while he sits in custody, turning the investigation into a maddening cat-and-mouse game. To celebrate those dramatic exonerations, the landlady arranges a party and a concert at the boarding house, turning the building into a stage where the tenants showcase their quirks and talents as the case edges toward its climactic twist.
Just before the party, Wens pieces together the pattern, and he nudges Mila to drop hints that he will be making an arrest that very night. In a cruel twist, the trio are not only linked by the murders but are revealed to have committed different killings in the same sequence, giving them each a plausible alibi for the others. They seize the moment to trap Wens and haul him to a nearby building, where they calmly explain that they intend to kill him and deposit his body in a vat of quicklime so that his fate will be forever hidden. They offer him a grim “compliment” for solving the case: the chance to name which one of them will deliver the fatal strike, each presenting a different weapon and a different method of celebrating their supposed genius.
They bicker at length about who deserves the principal credit for their collective ruse—their cleverness in pretending there is only one killer—while Wens observes with cool restraint. The tension breaks when Mila arrives, bringing a contingent of police who surge to the scene and rescue the inspector just as the would-be killers are about to finalize their plan. In a moment of neat reversal, the trap is sprung not by a single arrest, but by a coordinated rescue that reasserts Wens’s control over the situation and foils the twisted collaboration of the Durand group. The ordeal ends with a quiet insistence on justice, even as the lives tangled in the Durand case leave their mark on everyone involved.
