The Beast centers on an unorthodox but effective FBI veteran, Charles Barker, who takes on a rookie partner, Ellis Dove. Barker trains Dove in a hard-edged, psychologically driven approach towards undercover work, where a moment's hesitation can lead to death. Although Dove takes a liking to Barker, an FBI Internal Affairs team feels Barker may have gone rogue and they try to enlist Dove as a double-agent in the bureau's investigation of his mentor.