The Loner (1987)

Original title: Le Solitaire

In Paris , Commissioner Stan Jalard and Inspector Simon Lecache plan to quit the police to go and enjoy a more peaceful life in the West Indies. In a nightclub, during a routine visit, they spot Schneider, a dreaded gangster and public enemy. At the time of his arrest, Simon is killed at close range by the criminal. Stan then decides to stay in the police to avenge Simon. Being the godfather of Christian, Simon's son, who sometimes lives in a boarding school, sometimes at home, he takes charge of his education. Two years later, Stan has been promoted, and he's told that Schneider had resurfaced in the capital. A long hunt begins.