The Chosen One
NCIS: Los Angeles Season 4 Episode 13 (01/29/13)
When a police officer is shot while making a traffic stop. NCIS is called to investigate due to a possible terrorist threat. After finding ammonium nitrate in the abandon van, they investigate and track down the terrorist cell responsible. A member of the cell is flying into LAX that the cell doesn't know, so Callen takes his place and goes undercover. It turns out that he replaced the suicide bomber. After being fitted with the suicide vest, the cell leader lets on that he knows that Callen is a plant and they changed the plan. NCIS is able to figure out the change in plan in time to save Callen and prevent the bomb from going off.