On June 28, 1914, Archduke Franz Ferdinand and his wife are assassinated, triggering a sequence of alliances that plunges the world into war. But that is where the similarity ends. This global conflict is between the Clankers, who put their faith in machines, and the Darwinists, whose technology is based on the development of new species. After the assassination of his parents, Prince Aleksandar's people turn on him. Accompanied by a small group of loyal servants, the young Clanker flees Austria in a Cyklop Stormwalker, a war machine that walks on two legs. Meanwhile, as Deryn Sharp trains to be an airman with the British Air Service, she prays that no one will discover that she is a girl. She serves on the Leviathan, a massive biological airship that resembles an enormous flying whale and functions as a self-contained ecosystem. When it crashes in Switzerland, the two teens cross paths, and suddenly the line between enemy and ally is no longer clearly defined.
