With Vance splitting the team up after the death of Director Shepard, Gibbs finds himself with a whole new team investigating the murder of a high level Petty Officer who was selling classified information to someone within NCIS. He attempted to confess and reveal his source to Vance but was murdered before he had a chance. Unbeknownst to Gibbs, Vance intentionally split the team up so they could help gather intelligence on weeding out the mole/murderer within NCIS. McGee has been reassigned to run his own computer intelligence team in the sub-basement, Ziva is undercover in Israel and Tony is stationed on the USS Seahawk. The three suspects that Vance wants investigated, Lee (Jimmy Palmer's girlfriend) Langer, Keating and Lee all happen to be the new team that he assigned to Gibbs. When Gibbs learns of this he enlists his old team for help. Lee has an air tight alibi when Palmer confesses that all the times Lee suspiciously logged into the strategic planning office (where our dead Petty Officer worked) happened to be their secret rendezvous meeting place. While questioning Keating, Langer finds a stolen security clearance badge (belonging to our victim) in Keating's backpack and convinces Lee to go with him to check out the computer archives that the card accesses. While down in the archives, it looks as if Langer turns on Lee and tries to kill her. Lee calls Gibbs on his cell phone screaming that Langer is the mole. Somehow Lee is able to overtake Langer and shoots him with Gibbs, Vance and McGee showing up soon thereafter. In the end, the case seems closed until the audience sees in a series of flashbacks that Lee staged the whole thing, she's the mole.