S2·E13 Bloodlust

The bodies of badly beaten men are being found in the Boston metropolitan area. Sam and the team quickly surmise these men were involved in some sort of deadly ultimate fighting match. Searching local hospitals, they find a participant in one of the fights. Though he reveals little, Sam is able to put together from talking to him and researching the backgrounds of the victims, that all were desperate men in need of money. All the men have a bookie in common and the team eventually gets this man to confess his role in the murders. It turns out he supplies the names of these desperate men to a man who then manipulates them to fight for money. He then coerces them with drugs to fight to the death so that he can satisfy his own demented bloodlust. To catch the fight's mastermind in the act, John goes undercover as one of the fighters. The episode concludes with Sam and the team racing to find John before he too becomes a victim of this lethal bloodsport.