"It has served us well, this myth of Christ." (Pope Leo X, 16th Century)
Four masked horsemen, dressed as Knights Templar, storm an exhibition of Vatican treasures at the Metropolitan Museum of Art, stealing artefacts and beheading a security guard. Archaeologist Tess Chaykin sees their leader select a piece that turns out to be an ancient decoding device used by the Knights Templar.
Consequently, she becomes involved in an investigation in pursuit of her former colleague, William Vance, whose obsession is fuelled by the most personal of tragedies. Sean Reilly leads the FBI's investigation and Tess takes him through the dark history of the crusading Knights and on a journey which forces them through the sewers of New York, to the barren Turkish coastline and to the highest point of command at the Vatican. Their growing relationship plunges Reilly into a spiritual and professional conflict.
Meanwhile Vance's desperate wish to reveal the reason for the persecution of the Knights threatens to shake all modern religions to the very core.