1583.

William Constable, recently married astrologer and mathematician, has settled into routine work as a physician when he is requested to attend two prisoners in the Tower of London. Both are accused of separate acts treason, but their backgrounds suggest there may be a connection.

Sir Francis Walsingham and Lord Burghley urge William to discover further intelligence from the prisoners while tending their injuries from torture.

The agent’s investigations lead him to the French Embassy, which lies at the heart of a conspiracy which threatens the nation.

Through his enquiries, an unsuspecting William becomes entangled in a perilous web of politicking and religious fervour.

The threat comes, not from conspirators, but one of the most powerful men in the English court – one referred to as the Queen’s Devil. The fate of his family has become bound up in the revengeful spite of this man.

William faces a race against time to unpick these ties, climaxing in a daring raid on the Embassy.