The 1942 French film "The Murderer Lives at Number 21" ("L'Assassin habite au 21") is a comedy-mystery about a police inspector searching for a multiple murderer in the Montmartre section of Paris, France. The inspector receives information that the killer is living in a boarding house at "Number 21" and moves into the boarding house posing as a minister. The unknown murderer visits a construction site and then the company office. He shoots a man working there and steals paper money and coins from a desk.

The body of a man is found with a calling card.

The card reads "Monsieur DURAND" (Mister DURAND).

A construction site appears:

The construction company office appears:

A man is seated at a desk with papers on the desk and sees something in front of him. The murderer enters the office and shoots the man who falls under the desk. A closer look at the desk top reveals paper money and coins.

The currency notes appear to be close imitations of real French money of the period.

One coin has a head facing right and appears to be a French 10 franc silver coin.

Silver, 28.0 mm, 9.92 gm
Obverse: Head of woman facing right, REPUBLIQUE FRANCAISE
Reverse: 10 FRANCS 1934 LIBERTE EGALITE FRATERNITE
These coins were minted from 1929 to 1939

The killer removes a currency note.

The killer's calling card appears again.

Monsieur Durand has become infamous and French police officials threaten their subordinates with dismissal unless they find the killer. Police inspector Wens (Pierre Fresnay), Wens being short for Wenceslas, is at the bottom of the chain and is told that he has two days to catch the killer. Inspector Wens lives with his girlfriend Mila Malou (Suzy Delair), an aspiring actress and singer.

Wens tells Mila about his problem and she decides on her own to search for the killer. A man tells Inspector Wens that he found some of the calling cards at a boarding house named "The Mimosas" located at 21 Junot Avenue in the Montmartre district. The inspector, posing as a minister (not a priest) named Pastor Robert Lester, moves into Room 13 (he is not superstitious) of the boarding house. Mila also also moves in. Pastor Lester is introduced to the other boarders, the landlady Madame Point, Mr. Colin, a woodworker, and Dr. Linz, a retired doctor.

Pastor Lester then meets more residents, Mr. Colin and Dr. Linz.

Professor Lalah-Poor is a magician and occultist and usually wears a turban.

Mr. Colin has been selling faceless dolls as "Monsieur Durand." Pastor Lester visits the professor who lives in an Egyptian-themed room.

The professor asks the pastor: "What do you want to know?, The secret of the Hindu Tomb? The mystery of the Talking Skull?."

The boarders assemble for dinner.

Mila finds the body of tenant Mademoiselle Cuq in a bathtub and the police are called.

The policeman and the residents look at the body. This time the killer does not leave a calling card but a piece of a newspaper front page.

The Le Petit Parisien headline read "Monsieur Durand Continue" before the "Monsieur Durand" was torn out. Another article reads: "La Defense de Madagascar continue a Tamatave et Majunga." This refers to the 1942 battle of Madagascar.

Another tenant, a former boxer, has his "nurse" living with him and Pastor Lester visits her.

Lester asks nurse Vania about her sexy lingerie and she replies that her nurse uniform is unconfortable. Professor Lalah-Poor puts on a show at a local theater.

He has brought his assistant Christiane.

He places his assistant in a coffin, fires a pistol at the coffin, and then opens it. The coffin now reveals a dead man.

The body has a note attached.

Mila sings a song and while looking at the sheet music realizes who the murderer is. Wens also knows who the murderer is and is no longer posing as a minister.

Mr. Colin points a pistol at Wens and takes him to a construction site. Lila calls the police station.

Dr. Linz, Mr. Colin, and Professor Lalah-Poor tell Inspector Wens that they went to the same school a long time ago and where they formed a criminal pact. They explain that they took turns as "Monsieur Durand."

The three men are arrested.

Pierre Fresnay as Wens
Suzy Delair as Mila Malou
Pierre Larquey as Mr. Colin
Noel Roquevert as Dr. Linz
Jean Tissier as Professor Lalah-Poor
Huguette Vivier as Nurse Vania
Director: Henri-Georges Clouzot
Writers: Henri-Georges Clouzot, Stanislas-Andre Steeman
Based on the 1939 novel L'assassin habite au 21 by Stanislas-Andre Steeman