Sense of place. That's what China Miéville is able to infuse into his work. In Perdido Street Station, he brought New Crobuzon, a re-imagined London to life. In Iron Council it was the deserts of Bas Lag. And with The City & the City he's made believable two city-states that occupy the same physical space, Ul Qoma and Besźel. They maintain their sovereignty by enforcing strict cultural boarders so that citizens of the two city-states walking down the same street don't even see each other, let alone interact. And I have to say: I loved it. I loved everything about the book. Except the story. It's not that the book failed. The central conceit, of these two cities in the same space, works. It's that the final reveal of the plot, well, I just didn't buy.
Boiled down, The City & the City is a murder-mystery/police-procedural. The protagonist (Inspector Borlú) investigates the murder of a young woman (Mahalia), whose body was found in Besźel but may have been murdered in Ul Qoma. But the real star of the show is Miéville's worldbuilding.
Playing with linguistics and what I can only imagine was meticulous mapping and naming of streets and building and features, Miéville instills a believable sense of place. I mean, it's not to much of a stretch to see the commentary Miéville is making about life in modern metropolises (almost used "metropoli", but that's incorrect): ghettos, homelessness, poverty, ethnic segregation (Chiantown, Koreatown, here in San Francisco Hunters Point and Visitacion Valley), projects, crime, affluency. Just like the citizens of Ul Qoma "unsee" the people and cityscape of neighboring Besźel (and vice versa), inhabitants of major cities today commonly step over homeless like they never saw them, ignore corruption and violence, don't see urban decay, and dismiss that which isn't right in front of them. My self included. Cities are dirty places and beautiful places, but there's a certain amount of unseeing one has to do to live in a major city or you'll be overwhelmed by it all (or at least, that's the rationalization I use). I think Miéville tapped right into that, which made the story work so well.
That said, the set up doesn't seem that sustainable, which is why a third city-like entity is necessary in order to maintain the boarders: Breach. Breach is the organization that makes sure the boarders between the cities are maintained and disappears anyone who dares to break the boarders. If one were to claim that The City and the City wasn't a spec-fic novel, I'd mostly agree, except for Breach. These near mythic enforcers appear out of nowhere, are seemingly ubiquitous and witnesses can't recall what they look like. And they have fancy weird weapons that knock people out.
Breach exists because in reality, boarders are porous and frankly the two cities would end up as one if it weren't for the other supernatural powers of Breach.
At times, the protagonist's insights into linguistics and etymology didn't ring true and sounded more like the author infodumping bits of cultural history and information through a conveniently knowledgeable narrator.
Still even that worked in the story, even if I didn't buy it. What didn't make sense was the actual story:
So, an international tech company pays a member of the Besźel government (a guy named Buric) to secure ancient artifacts from a dig that's plot-conveniently only in Ul Qoma (even though that's not how archaeology of major cities work), artifacts which are plot-conveniently Exotic-Mysterious objects of dubious physics, which this international tech company covets so that it can do research and development. Never mind what the physics or what the artifacts really are or even what kind of R&D this tech company wants to do with the artifacts (I'm more or less okay with this smokescreen, because that's what it is; these are Macguffins, Red Herrings, plot devices to keep the reader distracted and the plot moving, it's just that these were so convenient and executed in such a bulky manner. So convenient, that if they didn't exist as they did, which they did for no reason explained in the book (like why Ul Qoma is artifact rich and Beszel isn't; just trust us! Suspend your disbelief!) then the whole plot would fall apart.
Anyhow, Buric, hoping to secure said artifacts, contacts crazy old professor Bowden who wrote about Orciny (the third secret city, a conspiracy theorist's wet dream; the Trilateral Commission of Beszel/Ul Qoma) to manipulate a student (Mahalia) into smuggling Ul Qoma artifacts over to Beszel, but ends up killing her cause she doesn't believe in Orciny anymore, but instead of turning him in, Buric and Tech Company cover up Mahalia's murder. I mean, what's an international Tech Company to do? How else can they get artifacts with dubious physics? I mean, there's no possible way that they could say team up with the University of the Prince of Wales in Canada and build a whole new research facility for the University to do the kind of research they wanted and still control products and patents gleaned from said research, as partners with the university. No, that never happens (Google-Stanford, MIT-Every Huge Tech Company, CalTech-Every Huge Tech Company).
See, I just didn't get why the international Tech Company didn't just Buy Their Way In. Happens all the time. And in fact that's the take away at the end of the book when they corner international Tech Company: "What are you going to do? Your Government will never prosecute/punish me." And then he literally flies off in a helicopter with the artifacts of dubious physics (Note: Bowden, who was on the pay roll, actually HAD an artifact of dubious physics ALL ALONG, and just never bothered to sell it off).
The fact that a big tech company went out of its way to initiate such a convoluted plot, well, it left the ending a bit lacking. A lot lacking.
Other than that, this book ruled.