From the publisher's description:
In 1310, Templar knight Conrad of Tripoli stumbled on a trove of writings documenting the early days and divisions of Christianity. The Catholic Church has kept this material hidden since the fall of Constantinople in 1453, fearful that its release would undermine the church's authority and rock the foundations of Christian belief. In the present, Mansoor Zahed, an Iranian motivated by revenge for the CIA killing of his family in the 1950s, is bent on finding the trove and releasing it to undermine Western religion and stability. Meanwhile, FBI special agent Sean Reilly visits the Vatican on a quest to find a document that may help in his effort to rescue his love interest, Tess Chaykin, who's been kidnapped.