The Templar salvation - Raymond Khoury

Constantinople, 1203: As the rapacious armies of the Fourth Crusade lay siege to the city, a secretive band of Templars infiltrate the imperial library. Their target: a cache of documents that must not be allowed to fall into the hands of the Doge of Venice. They escape with three heavy chests, filled with explosive secrets that these men will not live long enough to learn.
Vatican City, present day: In the Secret Archives of the Inquisition, to which no one but the Pope's most trusted secondi are allowed access, FBI agent Sean Reilly has no choice but to violate the trust he has earned. A vicious, uncompromising terrorist bent on revenge has kidnapped Tess Chaykin, and the key to her freedom lies in this underground crypt, in the form of a document unread for generations: the Registro Templari, a secret history of the infamous Templars that may reveal the explosive secret behind their centuries-old extermination-and in the process illuminate a lost corner of history and its colossal 21st century implications.
As the bodies pile up, Reilly soon realizes that this is a foe unlike any he has battled before. An urgent, pulse-pounding manhunt will take him and Tess from Jordan to Vatican City, Istanbul and the otherwordly landscapes and underground cave-cities of Cappadoccia, Turkey, as they follow the bloodsoaked trail of their enemy.