I've fallen slowly in love with Renoir's romcom 'La Règle de jeu' What is it about La Règle du jeu that got under the skin of French viewers so? The answer must be closely allied to why it retains such fascination. Presumably, it was viewed as a satirical attack on the morals of upper-crust French society, but "attack" isn't quite the word. Renoir is far too understanding of, and in some ways indulgent towards, the changeability of romantic attachments which drives his plot. It begins with lines from Beaumarchais" 18th-century comedy The Marriage of Figaro, presenting love as a winged creature which is necessarily designed to flit about. In the case of Nora Gregor's Christine, the Austrian wife of the Marquis Robert de La Cheyniest (Marcel Dalio), happiness seems permanently elusive. She's torn between the competing attentions of her husband, the dashing aviator André Jurieux (Roland Toutain), and even Renoir himself, in the role of a gregarious failed conductor called Octave. Robert, meanwhile, is reaching the end of a lengthy affair with Geneviève (Mila Parély), which everyone knows about except Christine. These are fickle passions, choreographed like farce, and climaxing in what resembles tragedy but is played with more or less a shrug. In the superb hunt sequence, the film's centrepiece, we hear scoffing reference to an accident during the previous season, when someone called Georges shot himself in the thigh and died. All present find this hilarious. If we laugh too, it's at their callousness, but this offhand moment is planted to prefigure the movie's strangely cold-blooded dénouement. When the various sets of lovers fall to chasing each other around the château - there's also a randy poacher who wants to make off with the gamekeeper's wife - there are threats, fights, even gunshots, but none of the other assembled guests are disturbed, carrying on blithely with their card games and gossip. Renoir depicts an indifferent society, tolerant of its caprices even at their wildest, but also dangerously blind to the faults that might tear it apart. The technical fluidity of the film-making, embracing many elaborate camera moves and virtuosic depth of field, has always received routine praise, but we need to look harder. In his new BFI monograph on the film, V F Perkins calls attention to some of the salient imperfections in Renoir's style, and how they make this puzzle-box of a movie all the more tantalising. Cramming so much detail into his mise en scène, and keeping tabs on so many skittering plot-lines, Renoir often sacrifices flawless cinematic grammar for a messy, unstable inclusiveness. The film's partly about a social order - it's orderly when it needs to be - but there may be no other alleged formal masterpiece which lets in such a whirlwind of disarray, and for such clear thematic purpose. If it were too polished an object - if comedy segued on cue into the headline-grabbing tragedy we're led to expect - it wouldn't be as special. Revisiting La Règle du jeu at the BFI after its latest poll success, and reading Perkins" book, the film's greatness clicked for me in all the ways I was hoping it might. Everything in it - not just the relationships, but also every character's presumption of their place in the scheme of things - is wobbling on a precipice. The prolonged shot of a rabbit in its death throes, and the charming revue show of am-dram ghosts jiving to Saint-Saëns's Danse Macabre, are clues that mortality is very much on Renoir's mind. It's the mortality of civilisation. His film may end in manslaughter, and in the apparent resumption of a rigid status quo, but it uncannily refuses tidy closure, waiting for a sequel Renoir knew was imminent. On September 1, it came.