The Murderer Lives at Number 21

Inspector Wens is on the trail of a serial killer who has committed four street killings in the space of a few months. The only clue is a visitor's card signed "Monsieur Durand" found at the scene of each murder. Wens receives an unexpected tip-off that the murderer is living in a boarding house. Disguised as a cleric, he takes a room in the boarding house and finds that lodgers to be a very strange bunch indeed. One of them must be the murderer.