It's set in the future in a rather despotic world.
Most people's main ambition is to get a card which allows them to use a huge shop - the shop is run by a group of brothers - there's a lot of sibling rivalry! It's all very hierarchal and how you're treated depends on the type of card you have. Having no card makes you a virtual outcast at the lowest echelons of society.
Feel the need to reread it but can't remember what on earth it was called