Blood Oath is a novel published in 2010 by Christopher Farnsworth. It centers on three main characters: Nathaniel Cade, a vampire more than 160 years old, currently bound by a blood oath to serve and protect the President of the United States; former Federal Bureau of Investigation Agent William Griffin, or "Griff," Cade's handler for more than 30 years, and Zach Barrows, a former White House staffer that is Griff's replacement. The novel focuses on a deadly new threat to the United States from a horrible biological attack. Development Farnsworth has stated that the idea behind this book came from the strange story of President Andrew Johnson's pardon of a man accused of being a vampire, as related by Robert Damon Schneck and Charles Fort. He reasoned that if this story was true, how powerful of an agent for the United States could that vampire become, and how much good would he be able to do? Plot summary An Army Ranger unit is reassigned from hunting an Al-Qaeda terrorist cell in Iraq, to suddenly a clandestine mission in the unstable Republic of Kosovo, with details classified by the army's superiors. The unit conducts surveillance and maintains a security perimeter on a pack of Serbian thugs as night falls. A mysterious operative is then brought before the Serbian pack's leader and attempts to bargain with them for a metal box marked with US Army stencils that was stolen in rioting at the country's embassy. The operative attempts to trade a large bag of money for the case. However, the leader refuses to honour the agreement and, despite clear warnings by the operative, has his men attack the figure. One of the soldiers, veteran sniper Specialist Wayne Denton, witnesses the unusual operative suddenly react inhumanly fast and strong and proceeds to systematically kill them all, expertly and withstanding no injuries. Denton tries to kill the leader when he believes he will escape, only to find the leader is similarly fast and avoids his shot. Enraged, the leader races up to Denton's position to kill him. The operative, finished with the pack, intervenes at the last moment and kills the leader - witnessing the fight between them up close, Denton realizes what he is seeing: the Serbians were werewolves, and the operative, as he leaves, reveals he is a vampire. The unit is sworn to secrecy and returns to its mission the next