Scrivener's Moon
Philip Reeve
 In a future land once known as Britain, nomad tribes are preparing to fight a terrifying enemy - the first-ever mobile city. Before London can launch itself, young engineer Fever Crumb must journey to the wastelands of the North. She seeks the ancient birthplace of the Scriven mutants. Scrivener's Moon is the sequel to A Web of Air, the story set centuries before Mortal Engines.