Two friends from the last war, Pierrot, a bar owner, and Gustave, a police inspector, are in contact with a notorious gang of racketeers in Montmartre. Tired of putting up with Albert the King's demands, Pierrot kills the gangster during a bar brawl. His first instinct is to flee, but on Gustave's advice, he turns himself in to the law. All things considered, he'll be safer in prison than exposed to the reprisals of the "underworld". Pierrot goes to trial. He was acquitted as having acted in self-defense. But his release leaves him open to the vengeance of Bob, one of Albert's accomplices. Pierrot narrowly escapes an ambush, but is finally able to rid himself of the threat hanging over him, thanks to the friendship of Inspector Gustave, and finally reunites with the companion of his life, Dora, who has never stopped trembling for him.