of running London's economy. London is officially ruled by an elected Mayor. The Lord Mayor is Magnus Crome, who is also the head of the Guild of Engineers. Like most Traction Cities, London is built on a series of tiers. This encourages the system of social classes, with the wealthier nobles at the top of the city and the lower classes further down, closer to the noise and pollution of the city's massive engines. Atop the whole of London sits St Paul's Cathedral: the only building known to have survived the Sixty Minute War. Plot The book starts with the traction city of London chasing and catching a small mining town called Salthook. Tom Natsworthy, a teenage Apprentice Historian, is sent, as punishment for skipping a chore, to the "Gut" of London, where captured Traction cities or towns are stripped of resources. Tom incidentally meets the Head of the Guild of Historians, Thaddeus Valentine, along with his daughter, Katherine. One of Salthook's residents, teenager Hester Shaw, attempts to assassinate Valentine, but Tom interferes and chases her. She reveals a disfiguring scar on her face and claims Valentine caused it, before escaping the London police through a chute. When Tom informs Valentine of her name, Valentine pushes him down into the chute. Tom and Hester recover outside of London within the Hunting Ground and, after an argument, they start following the city's tracks to reboard it. The pair eventually boards a small town called Speedwell, where the owner Orme Wreyland drugs them and plans to sell the pair as slaves for profit at a trading cluster. Tom and Hester escape from Wreyland, meeting a friendly airship pilot called Anna Fang, who takes them in her airship the Jenny Haniver to the neutral flying city of Airhaven where they can find passage to London. At Airhaven, they are then attacked by a cyborg "Stalker" called Shrike, who was sent after them by the London Mayor Magnus Crome to kill them and bring their bodies to him. Tom and Hester escape by stealing a hot-air balloon and drift over the Hunting Ground. Hester reveals that when she was a child, her parents were killed by Valentine as they would not give up an Ancient machine. Valentine then injured her and believed that she was dead. Hester escaped, and Shrike took care of her for most of her childhood. Despite the fact that Shrike