Okay, imagine four Londons that exist in parallel dimensions. They don't really resemble each other in any way except that they're all called London -- it's four totally different worlds. And they range in power from nothing to magic is everything. And magicians can switch through the Londons like they're stops on the subway. So our main character is a magician who's a smuggler, and he runs into a thief who just wants an adventure, but there's a plot afoot that might destroy them all. It was inventive and imaginative and different, and totally worth the read. :)