Pierre Lambert buys a bar in Pigalle and accepts to pay "protection money" to "Bébert le Caïd", a brutal gangster. Over time, Bébert raises his fare and, realizing Pierrot is reluctant to pay more, starts persecuting him. In the midst of an altercation with Bébert, Pierre kills him in self-defense. In a panic he goes to see Gustave Martinet, a police inspector, who has been his best friend since Pierre saved his life during the war. Gustaves advises him to turn himself over to the police, which he does. At the trial Pierre is acquitted but the mob does not forgive so easily...