As Ducky meets his new assistant, Gibbs takes the case of a Marine found impaled on a tree stump. The investigation uncovers the sale of decommissioned military weapons on the black market. Tony goes undercover and meets the buyer, only to stumble into an ATF operation. Working with ATF Special Agent Stone, Gibbs poses as a weapons supplier to complete the deal, only to be seriously wounded as Stone reveals herself as a corrupt agent working in the arms trade.