But when a half-bird, half-human creature known as the Garuda comes to him from afar, Isaac is faced with challenges he has never before encountered. Though the Garuda's request is scientifically daunting, Isaac is sparked by his own curiosity and an uncanny reverence for this curious stranger. Soon an eerie metamorphosis will occur that will permeate every fiber of New Crobuzon--and not even the Ambassador of Hell will challenge the malignant terror it evokes.