Tom felt the deck-plates shiver as the city's huge hydraulic Jaws came slamming shut
“It was a dark, blustery afternoon in spring, and the city of London was chasing a small mining town across the dried-out bed of the old North Sea.”
The book opens with London chasing the town of Salthook over the dry bed of the North Sea, into Europe (now known as the Great Hunting Ground).
Salthook is soon captured and dragged aboard. While assisting the head of the Guild of Historians, Thaddeus Valentine, and his daughter Katherine in searching for relics in the captured town, Tom saves him from a knife-wielding girl. The girl jumps off London to evade pursuit, and Valentine pushes Tom off as well.
“The town slewed to a halt, smokestacks snapping off and crashing down into the panicked streets, and then London's lower tiers blocked it from view and Tom felt the deck-plates shiver as the city's huge hydraulic Jaws came slamming shut.”
Tom and Hester have been thrown together. Truly-thrown out of a city on wheels that's left them stranded and starving in the middle of nowhere while it hares off after its prey. Hester is desperate for revenge, and Tom is only desperate to get back on board his beloved London.
Tom awakens on the bare mud of the Great Hunting Ground, a desolate wasteland stretching in every direction. The girl, Hester Shaw, is there. She claims that Valentine killed her parents, scarring her horribly, and starts following London's wheel marks to try and catch up to it. Tom follows her.