This novel is a departure from the overt fantasy of his Bas-Lag series and his recent young adult book, Un Lun Dun. The closest approximation to his previous work would be to King Rat, which, for all its fantastic elements, was essentially a modern urban thriller.
The review that follows is phenomenally vague, but The City & The City is an exceptionally clever piece of fiction, and I don't want to spoil it.
The protagonist is Inspector Tyador Borlu, of the Extreme Crime Squad. Mieville sets the book up like a murder mystery - the slightly-jaded Borlu must deal with incompetent superiors (and juniors), awkward bureaucratic processes and an aging, under-staffed department. If anything, it is a conscious replication of the vaguely-existential, non-Western mysteries that are currently quite trendy (and rightfully so).
The existence of a mystery, however, is the ultimate red herring. Although the plot - with its many twists and turns - is the sort of well-crafted, exceptionally-detailed masterpiece that we can now safely expect from Miéville, this book is not about the plot.
Nor, for all Miéville's work in capturing the tone and the style of Albert Camus or Milan Kundera, is this a piece of existential literature. Borlu is an engaging, empathetic character- but, again, that's almost incidental.
Instead, the closest approximation to The City & The City is actually vintage science fiction - the days of Bradbury and Asimov. The book is old-fashioned pulp - basic one-engine, two-twist science fiction.
Miéville has a fantastic, mind-bending concept. By following the mystery, the story teases it and then introduces it fully. We're then introduced, bit by bit, to the logical extensions of the story's core conceit - including its negative repercussions. We get a final twist at the end that resolves the conflict gives the reader a final, holistic view of the concept.
Stepping back from the distractions of the mystery and the characters, the progression of The City & The City is almost obvious. Of course Borlu goes where he does and winds up where he does - it is (again) only due to Miéville's immense skill as a story-teller that I never stepped back and thought about it. Despite a core conceit that's wildly impossible, Miéville never breaks the suspension of disbelief - when it comes to combining pulp story-telling and impeccable writing, he has his cake and eats it too.
To put an end to the vagueness, here's something specific. The City & The City is easily the best book I've read this summer, and possibly this year. Its genre-bending classification will invariably frustrate booksellers and award lists alike, but this is a new classic of any... every... classification.
What Miéville has done is simply this: take a simple creative idea - the stuff of any magazine story or Creative Writing 101 - and make it into a mind-bogglingly delicious novel. And the intricate plot? The empathetic character? The philosophical progression? He does those as extras - Miéville casually includes what most authors strive - and fail - to achieve. That's crossing the line from skill to genius.