Campana, a commissar at the drugs bureau of Paris police gets an undercover job in Nice to catch an Italian-French mafia boss. As he slips into the identity of a gangster's brother, who was already killed, he has to play the role of a loving husband with child - something that is not so easy for a confirmed single like Campana. Unfortunately American killers chase behind the Nice mafia clan too, in order to get control of French drug trades to USA.
Grégoire Lecomte, the unlucky actor anxious to find a "real job", goes to take a screen test for a role of a killer, but gets to mafiosi by mistake. He takes their don for a producer, and they mistake him for a hitman with whom they had an appointment. Deluded Lecomte signs contract with them. He is supposed to kill gun dealer Otto Krampe at his birthday party in Saint-Tropez by piercing him with a cap of the umbrella with a built-in syringe with potassium cyanide. Lecomte is not aware that it has to be a real murder.
Dressed as a clown, the clever rascal Grimm holds up the most secure bank of Montreal and takes 30 hostages. While confusing and ridiculing the police with his strange behavior, he calmly manages to rid the bank of a fortune. But then an unsatisfied companion arouses trouble...