Don and his team must stop a sniper who goes on a killing spree in Los Angeles.

Pressed for time to find the sniper, Don calls in a senior Sniper Instructor from Quantico (guest star Lou Diamond Phillips) to assist on the case, causing Charlie to feel insecure about his role as special consultant to the FBI. Feeling animosity towards Agent Edgerton at first, Charlie learns from him that human behavior could make his mathematical equations useless. Instead Edgerton encourages Charlie to get inside the head of the killer.