The CW just posted their synopsis of the final episode and can I say that it is totally spoilery, but OH Boy it is going to be a brilliant episode.

Episode 3.12: Jus In Bello
Airdate: February 21, 2008

AGENT HENRICKSEN CATCHES UP WITH SAM AND DEAN - Sam (Jared Padalecki) and Dean (Jensen Ackles) break into Bela’s (Lauren Cohan) apartment in order to get the Colt back, but she has tipped off Agent Henricksen (guest star C. Malik Whitfield) about their whereabouts and they are arrested. While Sam and Dean are locked in a cell in Colorado, a demon breaks in and kills some of the sheriff’s men and possesses Henricksen. After the guys vanquish the demon, the FBI agent realizes they were telling the truth and prepares to release them, but Ruby (guest star Katie Cassidy) shows up to a warn Sam and Dean that the jailhouse is surrounded by a band of demons with a powerful new leader who wants Sam dead.

Kim Manners directed the episode written by Sera Gamble.