The year is 1578.
"William Constable, a physician and astrologer, is summoned to the presence of the Queen’s spymaster, Sir Francis Walsingham. He is charged to assist a renowned Puritan, John Foxe, in uncovering the secrets of a mysterious cabinet containing an astrological chart and coded message. Together, these claim Elizabeth has a hidden, illegitimate child (an “unknowing maid”) who will be declared to the masses and serve as the focus for an invasion.
Constable must uncover the identity of the plotters, unaware that he is also under suspicion.
A connection to his estranged mentor, Doctor Dee, comes under scrutiny. Pressured into taking up a position as a court physician, Constable becomes a reluctant spy."