While working on a powerful new weapon for England, the country's first secret agent John Dee finds himself threatened from all sides. First, his secret plans are stolen, then his son is kidnapped by a vengeful enemy from his past. At the same time, Dee's wife, Jane, is sent by Queen Elizabeth I to console her cousin, Mary, Queen of Scots, as court advisors attempt to try her for treason.

But Jane suspects her assignment is much more than a visit from a sympathetic cousin. Is it possible that Elizabeth sent her to speed Mary to her death without the public trial that she knows will forever define the limits of royal power? Together, John and Jane begin to feel genuine sympathy for the Scottish queen and work to finish his invention, protect their son, and save Mary from the scaffold. But can they do that while remaining loyal to the English crown?