The Aeronaut's Windlass

Jim Butcher, the number one bestselling author of The Dresden Files, begins a new series set in a gloriously imagined world of noble families, marvellous technology and magic-wielding warriors.
Since time immemorial humanity has lived inside the Spires, habitats towering for miles over the dangerous, monster-inhabited surface of the world.
Captain Grimm of the merchant airship, Predator, was dismissed from Spire Albion's military in disgrace - now his ship and crew are all he has, and he's fiercely loyal to both. When the Predator is severely damaged in combat Grimm has only one choice - take on a clandestine mission for Albion's leaders, or stay grounded for good.
And even as Grimm undertakes this perilous task, he will learn that the conflict between the Spires is merely a premonition of things to come. Humanity's ancient enemy, silent for more than ten thousand years, has begun to stir once more. And death will follow in its wake . . .