L'inspecteur connaît la musique.

Harry Louis is a jazz clarinetist, obsessed by his art: he would like to match Sidney Bechet; the famous musician tries to give a piece of advice to his fan who, accidentally, kills him in a fit of anger. With the help of his mistress, Muriel, who has witnessed the scene, Harry does away with Bechet's dead body. But, during this gruesome trip, Muriel is accused of being responsible of a road accident. The insurance company sends a young man, Laurent, to investigate.