A well written but slightly silly mystery novel. The conceit is similar to a Vance short story, that the population of a city has split into two cultures which are physically intermingled but pretend not to see each other except in very formalized circumstances. Kind of like liberals and conservatives on FaceBook. The conceit is interesting and Mieville spends a lot of pages filling out its myriad practical details, but in the end I think he spends too much time on it. I enjoy the details, but when the idea is examined a bit more it does tend to fall apart rapidly. The conceit is also a little bit too familiar, both from Vance and from numerous video games which have a Light and a Dark world, or something similar. On the flip side, Mieville is a skilled writer and does a good job with the Eastern European politics and characters and the mystery itself. I think I would have preferred a straight up mystery novel from him rather than a mystery which plays with fantastic elements.