When Arthur decided to become a police officer, it sure wasn't so he'd have to hunt down a small group of ultra-left wing artists, the Black Fist Group, whose main activity is to stir up trouble. No, Arthur's thing was in fact to find his father, Public Enemy No.1, known as "The Malice." But, at the station where he works nights, its exuberant Captain Moulinette who sets the rules, backed up by his loyal lieutenant, sluggish Gégé. Arthur must hence obey orders and infiltrate the Black Fist. To do so, he pretends to be an actor, convincing their muse, the irresistible Blanche Rippolin, who then drags him into her nocturnal adventures. But at night, Paris isn't quite the same.