An adaptation of the novel by Georges Simenon, the film is set in La Rochelle, an ancient township in France, where you have to pass through narrow, ill-lit streets to get from one shopping area to another.

A number of old ladies have been found dead, strangled with the string of a cello. It soon becomes evident, that all of them had been raised in the same convent , and there is only one more to go: Armadine de Hautbois. The people of La Rochelle all have their own theories about the murderer, and so has Mr. Labbé the hatmaker, whose wife never leaves her bed, since she became crippled fifteen years ago. In a letter the strangler had written: "... there is only one victim left...", and so things should be coming to an end soon—but it's so easy to make mistakes...