Following a broadcast on the radio, each of the listeners remembers these "little nothings" (the title is borrowed from a play by Mozart), which have often changed their lives. Each of these stories told will prove that a tiny detail in life can change an entire destiny.

In the elevator of two large Parisian buildings, a telegraph operator discovers the body of an elderly woman, Madame Mathieu, the owner of both buildings. Boucheron (Lucien Baroux), the local superintendent, is dispatched to investigate, along with his rival, Inspector Lambert of the "Sûreté" (Jacques Baumer). To solve the enigma, they scour staircases and corridors, visiting every floor of both buildings, courtyard and facade. Their gruff rivalry allows them to complement each other in discovering who committed the crime among a gallery of characters, humble or rich, who all have something to be ashamed of... A rare, fast-paced, picturesque comedy set against the backdrop of a police mystery.

A man is a hunter at Maxim's restaurant. He lives in the provinces and his family is unaware of his profession. As soon as he has enough money, he quits his job and goes home for his daughter's wedding to a marquis. This one is a regular at the restaurant and the man tries to prevent the wedding before the truth is discovered.