London, summer of 1584: Radical philosopher, ex-monk, and spy Giordano Bruno suspects he is being followed by an old enemy. Instead, 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 of Canterbury, he agrees to do anything he can to help clear her name.

But in the city that was once England's greatest center of pilgrimage, Bruno uncovers a more dangerous plot in the making, one that forces him to turn his detective's eye to the strange case of Saint Thomas Becket, a twelfth-century cardinal of Canterbury Cathedral whose mysterious murder is only matched by the legend surrounding the disappearance of his body.