Tom and Hester finally make it to Airhaven with Anna Fang, only to be rudely interrupted by and evil machine sent by London named Shrike. This evil machine chases them through Airhaven whilst destroying the city.
Tom and Hester make it away from Shrike and head into a hot air balloon. They fly away for a bit but Shrike quickly catches up. To get him off their tail Hester lands the balloon, they get off, and she lets it fly up as a decoy.
Tom and Hester lose track of Shrike for a bit but are now on open Hunting Ground for cities. Shrike then catches up to them but is hit and crushed under a small city. Tom and Hester hop on a slightly larger city to avoid getting crushed, and are promptly captured and imprisoned.
Back at London, Katherine heads to the depths to try to find the engineer that saw the chase at the beginning of the book with Valentine and Hester. She doesn't find the man she wants but finds a interesting boy named Bevis who doesn't want to give her info just yet.
Tom and Hester are tied up in the dungeon of the city they hopped when they meet the city's mayor. Well not exactly the mayor, because he is actually the captain of a pirate town. Hester smooth talking and Tom's London ancestry get them out of imprisonment.
Katherine receives a note later from "a friend" to meet at a nearby cafe on London. She goes there and it's Bevis. He tells her everything. He was the engineer who saw Hester. The underground is killing workers. He has heard of MEDUSA. All this makes Katherine very curious.