The City & the City is a 2009 New Weird crime novel by China Miéville. Inspector Tyador Borlu of the Extreme Crime Squad of the decaying Ruritanian city-state of Beszel investigates a murder; his investigation turns international, and he ends up crossing over to Ul Qoma (a Singapore-like city-state, with some Turkish flavor and an embargo by the US) to continue his work. Ul Qoma happens to be geographically - grosstopically, to use the local phrase - in the same place as Beszel, but a completely different culture. There are neighborhoods of Ul Qoma that are exclusively Ul Qoman, and neighborhoods of Beszel that are exclusively Besz, but there are a number of locations that are 'cross-hatched' (part Besz, part Ul Qoman), in which, depending on which city-state one is in, one must unsee what is in the other city-state, for fear of Breach (a kind of secret police). There's also rumors of a third city, Orciny, between the two cities.
This novel provides examples of:
Ancient Conspiracy: Orciny is hinted to be this throughout the novel. It's a lie put forward by a self-aggrandising academic, sick of being put down for his Old Shame.
Cluster F-Bomb: Dhatt, oh Dhatt. "Even though of course those fuckers, those fuckers more than any other fuckers — and we have our share of fuckers." Also see his paragraph-long Cluster F-Bomb during his interrogation.
Decade Dissonance: For a long time, Beszel was far more technologically advanced than Ul Qoma, and the roads were filled with Qoman donkey traps alongside Besz motor cars. Now the situation is reversed, and Beszel is stuck with late-80s infrastructure - dial-up internet and rickety cars - while Ul Qoma is awash with skyscrapers and broadband. It's implied this is necessary for the separation to keep working - without being able to tell at a glance what city a building or vehicle belongs to, a citizen is perpetually at risk of Breaching.
Felony Misdemeanor: Breaching is a much worse crime than anything else that could be committed in either Besz or Ul Quoma, and the police invoke the omnipotent Breach to deal with the case of the murdered girl. When her American parents fly in to Besz, they're outraged that the police aren't investigating the case more thoroughly. They just don't understand that calling in Breach to deal with a case is akin to summoning God to enact divine retribution upon a wrongdoer - or, at least, that's how the two cities see it.
Grey and Grey Morality: There are lots of people who aren't very nice here, but the story is rather short on actual heroes and villains - in the end, it's impossible to say who, if any, of the many factions was in the right, or if there even was an 'in the right' at all.
I Choose to Stay: Borlu, deciding that he won't be able to unsee the cities after his stint with Breach, decides to join them and see both cities freely.
Jaywalking Will Ruin Your Life: Breach (The act of acknowledging the existence of the other city as well as crossing over into it illegally, in this case, but is also the name of the secret police) is treated as a crime worse than murder in Beszel and Ul Qoma. Adult citizens who cross over into the other city through unofficial venues are taken away by Breach (the secret police in this case) and are never seen again. Tourists are merely exiled permanently from both cities, and it's stated that children are also treated more leniently.
The Man Behind the Curtain: Breach. After being played up as a mighty, possibly-supernatural force of municipal vengeance for most of the book, they turn out to be little more than a small, moderately high-tech, and very human group who draw their 'powers' from the citizens' psychological blind spots and their recruits from the breachers they abduct. They only exist because Beszel and Ul Qoma allow them to, and the foreign Mega Corp. running the artefact smuggling ring holds them in contempt so complete that they're powerless against it.
Maybe Magic, Maybe Mundane: The artefacts, which are historical, deeply weird, and hinted to have functions and abilities of a decidedly alien sort... but never actually do anything explicitly supernatural on-screen. In accordance with the book's themes, no explanation is ever given, and the matter is not dwelt upon.
Mind Screw: So it's a crime thriller set in two cities that happen to occupy the exact same geographic location and are culturally mandated to be unaware of it? Go on... It only gets worse when you realize that the story contains no significant supernatural elements.
Misplaced Wildlife: Wolves live in the streets of both Beszel and Ul Qoma, but the scruffier and scrawnier variety is tacitly native to Beszel, while the larger and better-groomed wolves are supposedly native to Ul Qoma. When the (Besz) narrator shoos away a clean-looking wolf from his garbage, his neighbors act as shocked as if he had breached.
Schizo Tech: The artefacts found beneath the two cities, causing the archaeological teams investigating them no end of headaches.
Secret Police: Breach... Sort of. It's a faceless omnipotent magical/alien/divine law-enforcement thing that stops unauthorized crossing over between Beszel and Ul Qoma.
Selective Obliviousness: Citizens of Ul Qoma and Beszel are quasi-legally obligated to employ a kind of Selective Obliviousness at all times to avoid noticing the other city. Failure to do so results in Breach, a crime punishable by recruitment. Despite this, it's implied that the two cities' mutual selective obliviousness developed independently, and were responsible for the creation of Breach as a power in the city rather than the other way round.