Call of the Phoenix — Alex Woolf

An airborne invasion. A friend turned traitor. An empire in danger. Welcome to the second book in the thrilling steampunk series, Iron Sky!
Step into an alternative nineteenth-century England filled with giant airships, steam-powered automatons, aerial carriages, floating cities . . . and a new kind of secret agent. As Napoleon's forces mount a full-scale invasion of the country, Lady Arabella West and her mechanical sidekick Miles must face two deadly enemies: the Equestrians -- a terrifying army of iron centaurs -- and, worse yet, one of Arabella's own Sky Sisters, who has turned traitor. Can she and Miles save the British Empire from the forces that would destroy it?