Alain Delon's first effort as producer - though he'd dabbled in distribution for Any Number Can Win - was a box office failure, but is actually one of his best movies. It's a moody downbeat tale with Delon as a French soldier in the Algerian War who decides to desert; he gets the chance to go home if he helps the OAS kidnap a lawyer - but because she's good looking (Lea Massari) he falls in love with her, he helps her escape and now the OAS are after him.
That's a solid story, and its well executed, with plenty of atmosphere and exciting scenes (notably Delon's final moments, the abduction scenes, and facing off against the OAS).
The biggest problem is surprisingly the casting - Delon isn't up to the demands of the role; possibly it was his inexperience, or youth, or distractions of producer, but he's not convincing, particularly in the melancholy moments. I think he would have made more of a fist of it later on in his career - really it's a role that belonged to Jean Gabin or Charles Bronson.
Also he doesn't have much chemistry with Massari, who doesn't seem that in to him. The movie needs to be about a grand passion but they only display it occasionally. It would have been more exciting drama if her husband had had a more defined character; he's too weak dramatically. I feel it's the lack of fire between these two, rather than the political angle, which hurt the movie at the box office.