The prostitute Sarah is murdered by her pimp. The city planner Yann Moreau is confronted with the fact that the city is run by corrupt politicians. Nothing connects the lives of these two very different people, were it not for the 9mm gun, which is found in the stomach of Sarah's body. Nobody knows that Sarah's ghost lives within the gun. With the help of Yann, who involuntarily comes into possession of the weapon, Sarah declares war on the gangsters and corrupt politicians. A merciless fight breaks out, which could not be more brutal. Take the unbridled ferocity of a Luc Besson movie, mix in the best elements from Hobo with a Shotgun, Shoot 'Em Up and Crank and out comes the action firecracker Calibre 9.