Think of a city. Now, think of another city, one nearby whose culture, economics, and general life are completely entwined with the first one. Your mind may go to someplace like Minnesota's "Twin Cities" or perhaps Cold War Berlin, but think a little harder. What if the two cities actually overlapped each other so they shared the same physical space.
That's the basic idea underlying The City and the City.
One day a dead woman's body is found in Besźel, a city state somewhere in southeast Europe. Besźel shares some of its physical location with another city state, Ul Qoma. In some areas the two cities overlap (are "crosshatched"), requiring the citizens of each to learn to "unsee" the evidence of the other. A street in Besźel may be the same as a street in Ul Qoma, but the drivers in each city navigate it differently. Movement from one city to the other is restricted to a single border checkpoint. Murder is one thing, but the most serious offense in either city is to breach - to cross over to the other without permission - a taboo enforced by a shadowy organization known, coincidentally (and somewhat confusingly), as Breach.
Needless to say, the death of the young woman - from neither Besźel or Ul Qoma - requires our hero, a Besźel detective named Borlú, to dive into the mysteries of the two cities and, ultimately, of Breach itself. In other words, he winds up questioning the very fabric of his reality. China Miéville does a great job getting inside Borlú's skull, showing both the ingrained importance he ascribes to avoiding breach and his growing suspicion that it's all a bit daft.
There is, potentially, another city involved in all this, a city between the cities called Orciny. The murder victim is fascinated with Orciny and, just maybe, finds evidence that it exists and that's what got her killed. Only we wind up learning that the reason she was killed was much more mundane - a corrupt politician in bed with outside business interests - and the whole Orciny thing was just a means to string her along.
Similarly, Miéville kind of does the same to the reader. His premise that is inherently fantastic - as in a fantasy literature sense - yet he takes it and deconstructs it. However amazing the co mingled lives of Besźel and Ul Qoma are, there is nothing supernatural about their relationship. The citizens in each city merely learn not to see citizens in the other. Our brains have a powerful ability to not see what we don't want to see, but once the illusion is over it's over for good. Hence why Borlú, who gets as close to truth as there is in these places, can never really go back. Even Breach itself, which begins as some kind of "other" presence (possibly alien) turns out to be a sort of NSA plus SHIELD organization on speed.
By the end of things, to be honest, I felt as jerked around by Miéville as the victim had been by her killers. The only difference is that I loved every minute of it.
The City and the City
by China Miéville
Winner Locus Award, Aurthur C. Clarke Award, World Fantasy Award, & Hugo Award (shared with The Windup Girl)