Traction City — Philip Reeve

In a dangerous future world where gigantic, traction-powered cities attack and devour each other, London hunts where no other predator dares. Hidden in its vast superstructure is a murderous creature that severs the right hands of its victims. A rebellious young aviatrix and a secretive scavenger boy are about to come face to face with a robotic Stalker that is terrifyingly out of control.