Finch by Jeff VanderMeer
Finch is at least a couple of books in one. It's a detective thriller in the noir tradition. It's a novel of resistance and rebellion in occupied territory. It's other-world urban fantasy. Whichever one of those attracts you, read it.
John Finch is a detective in Ambergris, a city-state that's featured in a couple of Jeff VanderMeer's previous books (which I haven't read). It's a city occupied by the oppressive grey-caps, a race of something like walking mushrooms who took over the city a few years earlier. The essential otherness of all the non-human characters was conveyed well, and the organic technology and all-pervasive fungal growths were vividly imagined and described.
The novel opens with Finch being called in to investigate a murder he's not sure is a murder; he does get the feeling that if he gets it wrong (in the eyes of his grey-cap boss) then that will be the end of the road for Finch, so a lot is resting on this case. The detectives are toyed with by their fungal superiors, fed parts of the picture and left to flounder. Finch clearly has a Past, which we are allowed to glimpse gradually as we are let into the backstory of this city - civil war, long years of building aggression, spies and double-crosses, shifting temporary alliances. Betrayal.
As well as being a gripping adventure (a bit bloody in places but nothing gratuitous) this is a poignant and moving novel about friendship, trust and allegiance. What (or who) do you hold onto when everything else is lost? The souvenirs from a dead past that allow you to hold on to the last of your sanity.