a story which takes place twenty five or thirty years before Mortal Engines opens. It's set on London's lower tiers, where Mortal Engines barely ventures, and tells of how the sleepy routine of Airdock Green police station is disrupted, first by the arrival of a young aviatrix who may or may not be an Anti-Tractionist saboteur, and then by the news of something nasty lurking in the abandoned district called The Wombs.
There is also a follow up to Fever Crumb and Web of Air, 'Scrivener's Moon', being released on the 4th and 7th of April, in paperback and hardcover respectively. The Amazon description is as follows:
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. In the chaotic weeks before battle begins, Fever finds a mysterious black pyramid. The extraordinary secrets it contains will change her world forever. The seventh awe-inspiring adventure in the World of Mortal Engines series by a superb writer at the height of his powers.The two different covers can be seen here and here (the hardback cover is brilliant and creepy). There's also more information on Philip Reeve's blog (same link as above, just click on the 'Home' tab), and contains what seems to be the promise of another book - 'I woke up the other morning with the first few chapters of a new book in my head, which are about what becomes of Arlo after A Web of Air.'