Thick as Thieves - S1.E18

Nick and Amanda work to stop a casino theft, but fail. Amanda realizes the ringleader is Jeremy Dexter, a fellow Immortal and thief that she has teamed up with several times over the millennia. She doesn't want to give Jeremy up to Nick, who has other ideas. Nick is being accompanied by Interpol agent Nicolae Breslaw (from the Highlander episode "The Valkyrie"), who is out for revenge because his younger brother was gambling in a casino with his company's money when Dexter robbed the place, and killed himself afterward. Nick and Amanda eventually set it up so that Breslaw can "kill" Jeremy, but he refuses to. Nick has to do so instead, leaving Breslaw to believe Dexter dead so that the latter can sneak out of town on Amanda's money.