Mortal Engines by Philip Reeve
In the far future, after a series of cataclysmic wars, great cities lurch across a barren landscape, searching for smaller cities to cannibalize for supplies and slaves. Tom Natsworthy, an apprentice historian in New London, idolizes Valentine, the city’s chief archaeologist and hero. Unfortunately, he finds himself drawn into an attempt on Valentine’s life, which leaves him exiled from the city with only the would-be assassin, Hester Shaw, for companionship. Reeve’s grim future is absolutely fascinating and his characters are three-dimensional, deeply flawed, and powerfully endearing. This is the first book in a four book series.