Mortal engines Mortal Engines Series, Book 1.

Welcome to the astounding world of Predator Cities! Emerging from its hiding place in the hills, the great Traction City is chasing a terrified little town across the wastelands. Soon London will feed. In the attack, Tom Natsworthy is flung from the speeding city with a murderous scar-faced girl. They must run for their lives through the wreckage-and face a terrifying new weapon that threatens the future of the world.