The Murderer Lives at Number 21 (in French L'Assassin habite au 21) is a 1942 comedy thriller film directed by Henri-Georges Clouzot, starring Pierre Fresnay. It was made in France during the German occupation and adapts the 1939 book of the same title by Stanislas-André Steeman.
A Serial Killer prowls in Paris. On the body of his numerous victims, he always leaves a visiting card with the name of M. Durand. The police are under pressure, but have no leads. A junk man finds in a cupboard a stock of the killer's visiting cards, so he guesses that the murderer lives in the boarding house where the cupboard comes from. So he tells Inspector Wens, who starts a covert investigation at Number 21, Junot Avenue.
The Murderer Lives at Number 21 provides examples of:
- 13 Is Unlucky: When he infiltrates the boarding house, Wens stays in room no. 13. He says that it does not matter, because he is not superstitious.
- Alliterative Name: Mila Malou.
- Alone with the Psycho: In the end, Wens realizes who the murderers are, but Prof. Lalah Poor threatens him with a gun and brings him to a construction site, where the two other killers soon arrive.
- Appeal to Flattery: In order to save time at the construction site, Wens asks who initially had the idea of M. Durand, because he thinks only that one deserves to kill him. It appears that the three killers share the ownership of the idea, so they start arguing.
- At the Opera Tonight: Wens attends a performance of Prof. Lalah Poor. The outcome of the investigation happens during a show given by Mila Malou and the inhabitants of the boarding house.
- Calling Card: The murderer always leaves a visiting card with the name of M. Durand on the body of his victims. Justified: this is a trick used by the three murderers to make the police believe that there is just one killer instead of three.
- Can't Get in Trouble for Nuthin': When he is threatened by Lalah Poor, Wens spits on a policeman's shoes to be arrested, but the policeman drops the case because someone else calls for help.
- Casting Couch: Discussed Trope. Mila says "The casting couch is not my specialty!" when talking with the theater impresario. It's a dash of Hypocritical Humor, as earlier in the scene she was clearly coming onto him and getting nowhere.
- The Cavalry: Wens is goind to be killed by the murderers at the construction site, when the police and Mila Malou arrive to save him.
- Christianity is Catholic: Averted, surprisingly. In France just about all Christianity is Catholic, but Wens still chooses to impersonate a Protestant minister when getting a room at No. 21. He specifically states that he has a wife and children elsewhere.
- Cloud Cuckoolander: Many of them. Mila Malou is Wens's Manic Pixie Dream Girl. Prof. Lalah Poor is a Hindu-style magician, with a lot of quirkiness: for example, he hides inside a box in his bedroom. Mlle Cuq is deluded into thinking that she is a talented writer. Armand, the valet, constantly imitates the cries of birds.
- Cut Phone Lines: Someone cuts the phone line of the boarding house to prevent Wens from calling the police.
- Dead Man Writing: Subverted. Wens leaves behind an "in the event of my death" letter telling his superiors that the killer lives at 21 Junot Avenue. But his nosy girlfriend Mila steams it open, reads the contents, and moves into the boarding house, where Wens is very much alive (and not happy to see her).
- Delegation Relay: A series of phone calls starts at the top of the command structure and works its way down the various levels of the French police, with each underling in turn demanding that his underling catch the murderer in a time interval that gets shorter and shorter with each phone call. Finally the chain of phone calls gets to Wens's supervisor, who goes to call Wens, and finds a note from Wens on his desk promising to catch the killer.
- Distressed Dude: Wens is brought by Lalah Poor to a construction site, where the three murderers are going to kill him. Fortunately, Mila Malou brings the police there and saves him.
- Everybody Did It: Downplayed. The mystery is of which of the inhabitants of the boarding house is the murder. The Reveal is that three of them —Colin, Linz, and Lalah-Poor— were in it together, taking turns committing murders.
- Evil Gloating: The three murderers lose a lot of time gloating at the construction site, which finally saves Wens's life.
- Face Death with Dignity: Wens remains collected even when three murderers are about to kill him.
- Failed Audition Plot: Mila Malou fails a singing audition in the beginning. The recruiter tells her that he cannot hire her because her name is not famous enough. He tells her that he would immediately recruit a serial killer like M. Durand because he is famous. So, Mila Malou decides to unmask M. Durand to become famous.
- Fair-Play Whodunnit: All the clues discovered by Wens are instantly produced to the viewer. There is no supernatural phenomenon or Applied Phlebotinum.
- The Film of the Book: The film is an adaptation of a 1939 book of the same title by Stanislas-André Steeman.
- Foreshadowing: M. Durand's victims keep getting killed in differing ways—one stabbed with a Sword Cane, one shot to death, one stabbed by a regular old knife; another is strangled offscreen. This is a clue that there's more than one killer.
- Get into Jail Free: Turlot insults a policeman because he wants to be arrested to be protected from M. Durand.
- Hand of Death: Seen in a couple of shots, like the opening sequence where a hand enters the frame wielding the Sword Cane, or later in the film where a hand is seen reaching into the frame to cut the telephone line out of the boarding house.
- Intro Dump: Colin, Linz, Miss Cuq, and Lalah-Poor—all of the residents of the boarding house, that is, and suspects in the case—are all introduced to Wens and the audience in the scene where Wens, undercover as a pastor, arrives at the boarding house and asks for a room.
- Lovely Assistant: Prof. Lalah Poor has one in his show.
- Manic Pixie Dream Girl: Wens is calm and serious. His job is to investigate murder cases. His girlfriend, Mila Malou, is a would-be singer with an exuberant personality. For example, she decides to start her own investigation of the M. Durand case. Later, she does not hesitate to follow Wens in his infiltration mission in the boarding house.
- Mr. Smith: The pseudonym of the serial killer, M. Durand, is a French equivalent. "Durand" is a very common family name in French. In the book, which is set in London, the pseudonym used is Mr Smith.
- Old Maid: Mlle. Cuq, the old lady at the boarding house, seems oddly proud of her elderly virgin status, calling herself a "maiden" more than once.
- Screw the Rules, I Have Connections!: When Mila Malou is arrested, she rapidly says that she is Inspector Wens's girlfriend to stay out of trouble.
- Serial Killer: A serial killer prowls in Paris. Unlike most serial killers, he seems to be killing for money and fun rather than some psycho-sexual compulsion, making this trope strangely blended with Gentleman Thief. On the body of his numerous victims, he always leaves a visiting card with the name of M. Durand.
- Setting Update: The plot of the original book was set in London. The action of the French film happens in Paris.
- Stage Magician: Prof. Lalah Poor is a Hindu-style stage magician.
- Sticky Fingers: Prof. Lalah Poor often steals items from the pockets of the other characters and immediately gives them back, like the wallet of Wens or the handcuffs of the policemen.
- Sword Cane: Dr Linz uses one.
- Title Drop: A petty criminal tells Wens "That's where the murderer lives, at number 21". He collected an old chest of draws that contained M. Durand's infamous Calling Cards.
- Workplace-Acquired Abilities: Prof. Lalah Poor is a stage magician, so he has Sticky Fingers: he is able to steal items from the pockets of other people. That comes in handy when he has to seize Wens's gun to prevent him from telling the police who the killers are.
- Writers Suck: Mlle Cuq is a would-be writer and is ridiculed. At some point, she even considers writing a detective novel with a plot very similar to The Murderer Lives at Number 21.
