|Season 5, Episode 21|
|Air date||1 May 2009|
The Fifth Man
Charlie, still feeling guilty about Don's injury, focuses on finding a frighteningly intelligent serial killer who is meticulous about eliminating all witnesses to his crimes, thereby murdering unobserved and undetected.
- There is a dual sense of the inhumane behavior of the killer and the perturbation of Charlie's worldview brought about by his awareness of Don's mortality and his own fallibility.