Perdido Street Station by China Mieville
This amazing book is set in a nightmarish fantasy city where the Parliamentary government has fascist police-state control over the citizens, and a blend of early technology (computer punch-cards, flintlock pistols) and magic (thaumaturgy) is commonplace.
The citizens themselves are an exotic mix of humans, cactus-people, women with giant scarab-beetle heads, garudas (bird-people), and others – including the Remade, or humans that have had their physiology altered to include machinery in the “punishment factories” because they have been convicted of a crime.
A hedonistic scientist Isaac is approached by a garuda who has had his wings cut off in punishment for a mysterious crime. The garuda hires Isaac to come up with a way to enable him to fly again. Isaac, investigating the properties of flight, inadvertently gets hold of a strange caterpillar that grows into an interdimensional moth that feeds on the dreams of humans. This moth helps to free four others of its kind that are being held as a secret government weapon, and this unleashes indescribable horror upon the city.
The corrupt city officials cannot contain the danger even though they attempt to bargain both with the Ambassador to Hell for the demons’ help (the demons are too scared to help), and a huge interdimensional spider who helps to spin the web of fate – an entity known to the garuda as the Mad Dancing God. It’s up to Isaac (and a few outlaw companions) to come up with a solution based on his life’s work in “crisis theory”. A startlingly original work of imagination