The story begins when Isaac Dan der Grimnebulin, a human scientist, and Lin, his alien lover, receive a visit from an exiled Garuda named Yagharek. Garuda are winged creatures for whom flight is as necessary as breathing. Yagharek, for reasons he cannot quite explain, has lost his wings, and commissions Isaac to restore them. In accepting this commission, Isaac sets in motion a complex plot encompassing a potent hallucinogen called “dreamshit,” a deadly, moth-like insect that feeds on dreams, and assorted denizens of the city’s colorful — and dangerous — underworld. Dominating this vast canvas is New Crobuzon itself, a profusely detailed metropolis.