Reeve, P: Web of Air (the Fever Crumb Trilogy, Book 2)

Two years ago, Fever Crumb escaped the war-torn city of London in a traveling theater. Now, she arrives in the extraordinary city of Mayda, where buildings ascend the cliffs on funicular rails, and a mysterious recluse is building a machine that can fly. Fever is the engineer he needsNbut ruthless enemies will kill to possess their secrets.