Sinners of Paris (1958)

Le Fondu, a famous gangster, escapes from the hospital where he was detained, killing an inspector in the process. The colleague of the deceased inspector, Paul Vardier, vows to avenge him. The task seems hopeless: Le Fondu has disappeared without a trace and nobody has a clue about his hide-out. There is only one faint possibility left: coerce Le Fondu's nephew into becoming an informer. Paul gets assigned as buddy Gilbert Barot, fresh from the police academy, and whose alluring wife Lucie quickly arouses the interest of Paul. Paul is quickly led to play two dangerous games simultaneously seducing the wife of his colleague, and tracking with him Le Fondu, who himself does not remain inactive...