London, summer of 1584: Radical philosopher, ex-monk, and spy Giordano Bruno suspects he is being followed by an old enemy. He is shocked to discover that his pursuer is in fact Sophia Underhill, a young woman with whom he was once in love. When Bruno learns that Sophia has been accused of murdering her husband, a prominent magistrate in Canterbury, he agrees to do anything he can to help clear her name.

In the city that was once England's greatest center of pilgrimage, Bruno begins to uncover unsuspected secrets that point to the dead man being part of a larger and more dangerous plot in the making. He must turn his detective's eye on history on Saint Thomas Becket, the twelfth-century archbishop murdered in Canterbury Cathedral, and on the legend surrounding the disappearance of his body in order to solve the crime.