1601. Queen Elizabeth I dies without an heir. The main candidate for the throne is King James VI of Scotland, but there is one problem. The Queen's spies - hardened by long religious wars - fear that Jacob is not who he claims to be. He argues that he is faithful to Protestantism, but perhaps secretly professes Catholicism, in which case forty years of suffering will be in vain, which threatens new bloodshed. Time is running out, and London faces an almost impossible question: how to check what Jacob really believes? And then the queen's spy Jeffrey Belloc finds a way to penetrate the soul of the future king.