Without a Trace (2002) : 5x8

Jack and the team investigate the disappearance of Alex Stark after his girlfriend reports him missing, and soon learn that Alex didn't own a cleaning business like he said he did but was actually involved in an illegal gambling operation. Jack goes undercover at a club that Alex would gamble at to find out what happened to him, and ends up being taken hostage by an associate of Alex's who becomes convinced that Jack is actually there to kill her. Unfortunately for Jack, his team believes that he has changed his cover story and has no idea that he's actually been kidnapped.