The City & the City by China Mieville
A masterpiece, and the standout of Mieville's already extraordinary literary oeuvre. A noird police procedural unlike any other, built on the highly original premise of overlapping societal borders, and the ontological bureaucracy created to maintain those boundaries. Set grosstopically in the interstices between Eastern Europe and the Middle East, the cities of Beszel and Ul Qoma become a wide-ranging crime scene for Inspector Tyador Borlu, who must solve a murder mystery whilst treading the silken social conventions that keep the two cities apart. Highly recommended.