Taking place in an alternate, war-ravaged version of 1914, the story centers on Alek, a prince on the run from the Austro-Hungarian Empire, and Deryn Sharp, a brave young woman who poses as a boy to enlist in the British Air Service. After their paths cross on the HMS Leviathan—a colossal living airship constructed from bioengineered creatures—they set off on a globe-spanning journey that forces them to reconsider their views on conflict, allegiance, and self.