While traveling across the United States during the Papal Symposium, the papal plane, Shepherd One, is commandeered by a terrorist cell calling itself the Muslim Revolutionary Front. On board: a nuclear payload with half the yield that destroyed Hiroshima. Their demand to the U.S. government: assassinate the five leading principals of Mossad. While the American leadership is forced to follow through with a proposition that would cripple the intelligence network between the allies, Pope Pius XIII is not without his own weapon. On board Shepherd One is his personal valet, a man who is the leader of a clandestine op group of elite commandos known as the Vatican Knights. His mission: retake the plane and remove all hostile opposition. Using his very particular set of skills, Kimball Hayden must neutralize the situation before thousands of lives are lost, including that of Pope Pius XIII.