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. Source: Wikipedia (en)