Children of the flying city

"Brought to the flying city of Highgate when he was only five years old, orphan Milo Quick has never known another home. A massive armada has surrounded Highgate's crumbling armaments. Because behind locked doors . . . the once-great flying city protects a powerful secret, hidden away for centuries. One small airship, the Halcyon, has slipped through the ominous blockade on a mission to collect Milo--and the rich bounty on his head--before the fighting begins"--Provided by publisher.