Proud, eccentric, and antisocial, Monsieur Hire has always kept to himself. But after a woman turns up dead in the Paris suburb where he lives, he feels drawn to a pretty young newcomer to town and discovers that his neighbors are only too ready to suspect the worst of him.

Gino Fabretti is a famous Italian tenor. During a tour in Nice, he begins a relationship with the wife of a renowned doctor. The doctor traps and drugs him and replaces his vocal cords with those of Robert, a delivery boy in a grocery store. Robert wakes up with the voice of Gino and Gino with that of Robert (including accents and mannerisms!). The unfaithful wife despises the tenor without his voice and becomes more interested in the grocer.

A jealous wealthy landlord intercepts a letter to his wife written by her cousin. He decides to take revenge by drugging the young man's horse, but it is his own son who will be the victim of the accident.