There'll always be a London: Philip Reeve, Fever Crumb (London: Scholastic, 2009).
Very good indeed. A prequel to Mortal Engines, it only slides into prequel mode very occasionally. Most of the time it is firmly its own book.
Fever Crumb has grown up in the Engineers' house shortly after the collapse of the Scriven rule of London. The Scriven were not quite human, and their inability either to breed true or to breed well with humans eventually led to their downfall and to the Patschkin riots.
On leaving the Engineers for the first time, Fever discovers she herself is at least part Scriven, but this becomes a minor issue as the nomads advance on London, and the archeologists and engineers look for the secret which the Scriven left behind.
Although there are some big themes, this is a slight novel, and most of its pleasures are in the discovery of the run down future London. It's nice to see an sf writer for kids keeping firmly to sf as well, the moment at which the book could have gone all mystic, science and scientific exploration comes firmly to the fore.