Two opposing forces are on the brink of war. The Clankers
- who put their faith in machinery
- & the Darwinists
- who have begun evolving living creatures into tools. Prince Aleksandar the would-be heir to the Austro-Hungarian throne comes from a family of Clankers & travels the country in a walker a heavily-fortified tank on legs. Meanwhile Deryn Sharp a girl disguised as a boy works for the British Empire crewing the ultimate flying machine: an airship made from living animals. Now as Alek flees from his own people & Deryn crash-lands in enemy territory their lives are about to collide...