As the nineteenth century draws to a close, most of Europe is in political turmoil, and terrorist threats loom large across the continent. Adding to this unrest is the controversial Sofia Delacruz, who has come to London from Spain to preach a revolutionary gospel of love and forgiveness that many consider blasphemous. Thomas Pitt, commander of Special Branch, is charged with protecting Sofia - and shielding Her Majesty's government from any embarrassment that this woman, as beautiful as she is charismatic, might cause.

When Sofia suddenly vanishes, and two of her female disciples are gruesomely murdered, Pitt is challenged as never before. Is Sofia's cousin, wealthy banker Barton Hall, somehow involved? And why has handsome cricket star Dalton Teague insinuated himself into Pitt's investigation?

Fearful that this sensational crime may trigger an international incident, Pitt welcomes the help of three allies: his clever wife, Charlotte; her great-aunt Lady Vespasia; and Victor Narraway, Pitt's friend and former commander at Special Branch. From the narrow streets of Toledo and a lonely monastery high in the hills of Spain to the halls and wharves of London, Pitt and his friends race against time in their desperate bid to catch a murderer.