NCIS: Season 4, Episode 21

4 - 21: Brothers in Arms

Director Shepard meets an informant named Troy Webster who has information on international arms dealer La Grenouille but Webster is killed. Shepard later becomes convinced that La Grenouille ordered the kill but the team are all doubting her judgement, believing she might be on a personal revenge trip which is further increased when she manages to lead the team into a trap, leaving them with no clues to La Grenouille's whereabouts after days of investigations.