Dee is in a race to save the Empire with the help of a mysterious manuscript offering global power in this continuation of the "lively" (The New York Times) Agents of the Crown series.

With rumors of the end times swirling, philosopher and astronomer John Dee travels to Prague in an effort to prevent one of Catherine de Medici's seductive ladies-in-waiting from luring the Holy Roman Emperor into a crusade against England.

To convince the famously occult-loving Emperor to join his side, Dee entices him with the esoteric Book of Secrets, a volume that, if decoded, could provide the chance to control the levers of heaven and earth. But Dee faces enemies at every turn, including a female codebreaker who could be the undoing of Dee and England itself.