Three little criminals get a tip for a great coup with lots of money in it. Unfortunately they lack the starting funds to buy the required welding torch. So they persuade their successful colleague Alphonse to join their team. But the well thought-out coup fails, and Alphonse is the only one of them who ends up in jail for several years. When he's released, he's out for revenge.
Acting
Aznavour's twitchy desperation vs Ventura's simmering menace
Direction
Granier-Deferre's cramped Parisian interiors, all elbows and bad decisions
Writing
Dialogue that sounds improvised, probably wasn't

Director
Pierre Granier-Deferre
Trivia, insights & behind the scenes
This came out the same year as Alphaville and Pierrot le Fou, but Granier-Deferre was playing a different game—more Melville-adjacent than Godard-revolutionary.
Aznavour was already massive as a singer; Ventura was the bigger box office draw. Their chemistry here reportedly came from genuine mutual suspicion.