When a Marine is killed with a specialized military weapon, the agents investigate the illegal weapons market and find an undercover ATF agent (Bellamy Young) also working on the case, and Gibbs asks her to work with them to find the killer.

Gibbs' obsession with finding the terrorist Ari (Rudolf Martin) reaches its zenith, and is timed perfectly, as Ari is training men for an attack on Marine One with President Bush and Prime Minister Sharon on board.