The peace forged by the love between Zane and Danica, leaders of the avian and serpiente realms that had been at war for generations, is threatened by the arrival of Syfka, an ancient falcon who claims one of her people is hidden in their midst.

While fifteen-year-old Ellie tries to find her missing eleven-year-old brother, Danny, in alternating chapters Danny dreams of a parallel quest in a fantasy world of dragons and shapeshifters that he and Ellie knew as children.

In an alternate 1914 Europe, fifteen-year-old Austrian Prince Alek, on the run from the Clanker Powers who are attempting to take over the globe using mechanical machinery, forms an uneasy alliance with Deryn who, disguised as a boy to join the British Air Service, is learning to fly genetically-engineered beasts.