I finished reading China Mieville’s The City and the City yesterday. Frankly, it’s a wonderful book and you should all go and buy it right now, if you haven’t already.
To go into it at slightly greater depth, the central conceit (that of two cities, Beszel and Ul Qoma, sharing largely the same geographical space due to some long-past dimensional weirdness, in which citizens of one must “unsee” citizens of another in shared areas not wholly in one or the other for fear of bringing the mysterious and terrifying Breach down on them) is brilliantly handled, interesting, and entirely believable, while the central characters and the storyline are top notch. If I had to nit-pick it would be that the villains of the piece get very little screen time so you never really see/understand/go “Aha! I knew it was them!” about their villainy, but it’s a piffling thing. (And one that I’m very familiar with - both Cregan books suffer/ed from it to one extent or another.)
Go and buy it.