The FBI is called in to help investigate a series of home invasions, and while trying to bust up one of the robberies, Don suffers a life threatening stab wound. Charlie, whose math had led to the raid, takes this news particularly hard because his calculations had only predicted that four assailants would be involved, leaving the team with their guard down when a fifth man attacked Don. With Don clinging to life in the hospital, David takes control and is able to ID one of the suspects, but is confused when they discover he doesn't fit the profile of a hardened criminal. Meanwhile, Charlie obsesses over his mistake and works harder then ever to catch the remaining robbers. His math helps set up a sting where the team is able to take the rest of the attackers in to custody, and Charlie's original prediction that the crew consisted of four men is proven correct when only three robbers show up on the scene. Charlie then discovers that the robbers had actually been looking for the fifth man, and had only been staging the robberies in order to find him. It turns out that the four men in the crew were all from the same Serbian village, and that the fifth man, Radovic, had been responsible for ethnic cleansing there. They had discovered the war criminal was in Los Angeles and in order to get justice, had tried to take matters in to their own hands. In the end Don pulls through, and the team is able to take Radovic in to custody.
