December 1585: King Henry III of France is the last of his line. He has appointed a Protestant as his successor, which has caused a three-way war in his country. As a result, the king is in mortal fear of a coup being orchestrated by the ultra-conservative Catholic League.

Radical philosopher, ex-monk and spy Giordano Bruno, forced to return to Paris, is called upon by King Henry to unearth the motivation behind several mysterious but linked deaths. Each victim is connected to a larger plot to manipulate the royal succession; what they knew and who killed them is a mystery to be solved.

Meanwhile, Bruno makes an uneasy alliance with Charles Paget, a key figure in the community of English Catholics who tried to assassinate Queen Elizabeth. When Bruno is implicated in the death of Leonie, a member of the Queen Mother's "Flying Squadron," he is forced to call on Paget and his connections for help--and finds that it comes with a price, involving an old enemy.