Twelve years into Elizabeth I's reign, the pope declares her a heretic giving England’s Catholics permission to kill her. The Queen looks to her spymaster William Cecil to stop the assassins getting through. Cecil establishes a huge espionage network, England's first secret service. Soon his focus falls on her cousin, Mary, Queen of Scots. Cecil knows Mary must die if Elizabeth is to live.

Robert Cecil is the son of Elizabeth I's original spymaster. He has been groomed since birth to inherit his father's network. But when he finally steps into his father's shoes, the Queen's enemies are stronger than ever. The Earl of Essex has established a rival network and is trying to oust Cecil as Elizabeth's spymaster. To survive, Cecil must ruthlessly maneuver Essex to the execution block.

Elizabeth I is dead and King James of Scotland travels south to take the throne at the invitation of Robert Cecil. Meanwhile, an extremist called Guy Fawkes, has a plan to blow up parliament with the King inside. Cecil hears about the gunpowder plot but is unaware of when and how they will strike. His investigation is hampered by the wildly ambitious plans of the new King.