Behemoth (Leviathan)

This book continues the hard-driving, action-packed adventures of Alek, heir to the throne of the Austrian empire and current British prisoner of war, and Deryn Sharp, a midshipman assigned to the Leviathan. Their loyalties to their respective governments and philosophies are tested as their friendship grows; Alek is an Austrian Clanker and Deryn an English Darwinist. After the Leviathan is damaged by a German attack, Alek and his personal guard escape the airship and join a revolutionary group dedicated to the overthrow of the sultan of Istanbul.