Two low level goons rob a card game run by the mob and, by making off with the wedge, apparently cause the city's 'criminal economy' to collapse.
It's a rather heavy metaphor of American economics and the wealth divide that comes with unshackled capitalism, set in 2008 the Bush/Obama electoral race plays out in the background to reinforce this. The plot of the film itself is an obvious micro-study of America's wobbly fiscal position, Brad Pitt's final sentences in the film sum it up well.
Although set in recent times, the film seems to make a strong effort to look like something from past decades. Aside from the election race footage (seemingly on every screen passed in the film) there is one brief shot of a mobile phone, everything else: clothes, hairstyles, cars, even the weapons used are far less era specific, giving the film a drab 1970s look. The retro look suits the film's throwback vibe, it's far more about dialogue and acting than crash-visuals and violence fetishism. Y'know, like film's used to be.