Here we have yet another euphemism for nark in French underworld slang -we have already encountered La Balance and Le Cousin - which appears to possess an endless supply of same. 'Doulos' means both 'hat' and 'informer' on French streets and given the subject matter plus the trade of the leading character it is well named. Jean-Pierre Melville was, of course, both a specialist and master of American-style French gangster films and here he does both himself and his American Masters proud. At this time he was still shooting in Black and White which enhanced the resemblance and homage to such U.S. titles as 'The Asphalt Jungle', Melville's personal favorite, though when he DID go with color he turned out two masterpieces in 'Le Samourai' and 'Le Cercle Rouge'. He tended to work with actors repeatedly, specifically Alain Delon - Le Samourai, Le Cercle Rouge, Un Flic - and Jean-Paul Belmondo, who even played a priest for Melville in Leon Morin, prete. It's Belmondo who gets to bat this time out and when he steps up to the plate he hits one out of the park. He is established tidily as a nark and Melville daringly delays until two thirds of the way through to reveal what is arguably the biggest twisteroo. To say more would be superfluous. Go see. 8/10