Michelle Lee was an NCIS Special Agent who was temporarily the "probie" of the NCIS Major Case Response Team and who was later revealed to be the NCIS mole leaking highly sensitive and classified information to an unknown source.
Michelle Lee made her debut appearance in the Season 4 premiere episode, Shalom (episode) where after Gibbs's departure and his senior agent, Anthony DiNozzo being made leader, Lee was brought in to bring the team back up to full strength following Gibbs's resignation in the aftermath of the Cape Fear disaster.
Following Gibbs's return in Escaped (episode), the team returned to their original positions and Lee was removed from the team for good, eventually being assigned to the NCIS legal department where she was frequently seen delivering warrants to the team. She even helped the team expose a major human trafficking-ring during the Season 4 episode, Once a Hero (episode) where it was also revealed that she was fluent in Chinese.
Lee was also a Harvard Law School graduate with the later episodes of Season 4 revealing that she was involved in a secret relationship with NCIS Medical Assistant James Palmer. NCIS creator Donald P.. Bellisario later told Australian magazine TV Week that the supposed relationship wasn't a relationship, just sex.
In the Season 5 finale episode, Judgment Day Part 2 (episode), following Director Jennifer Shepard's death, newly appointed Director Leon Vance broke up Gibbs's team of DiNozzo, Special Agent Timothy McGee and Mossad/NCIS Liaison Officer Ziva David, resigning the three elsewhere. Vance then brought in Lee and agents Brent Langer and Daniel Keating as replacements for Gibbs's new team but despite their best efforts, the "B" team as Dr. Donald Mallard called them did not live up to their predecessors's expectations.
During the Season 6 premiere episode, Last Man Standing (episode), upon realizing that Vance hadn't broken up the team because of Jenny's death, Gibbs confronted Vance with Vance telling Gibbs that the reason for his actions was because there was a mole in NCIS who was revealing highly classified US military information and that Lee, Langer, and Keating were the suspects with Vance having chosen to place all three on Gibbs's team to keep them under close scrutiny and determine which one of them was the mole.
The investigation took an intense turn when Vance learnt that the file that murder victim, Petty Officer Steve Vargo was Domino, the Joints's Chief battle plan in the event of an attack on a city in Israel.
After Langer's death at Lee's hands with Lee claiming self-defense and accusing Langer of being the mole, it was revealed that Lee herself was actually the mole, having killed Langer to protect her cover.
The incident went unnoticed for some time up until Collateral Damage (episode) where Gibbs began to suspect that it was Lee, not Langer who was the mole.
With Vance's approval, Gibbs launched a plan to expose and trap Lee. The plan was successful although it drew anger from DiNozzo who hadn't been of the plan but Gibbs later revealed the truth.
After being caught, Gibbs interrogated Lee where after confessing to being the mole, she told him that her reason for doing so was due to the fact that she was acting under duress as her daughter, Amanda Lee had been kidnapped and was being used as leverage, forcing Lee to commit the acts or else risk losing her daughter for good.
- "Do it."
- —Lee's silent message to Gibbs during the Season 6 episode, Dagger.
Lee died in the Season 6 episode, Dagger (episode) where while aiding the NCIS team, Ted Bankston, the true mastermind behind the entire operation and who sought Domino responded by taking Lee hostage with Gibbs following them.
Armed with the gun he'd stolen from an NCIS agent, Bankston with Lee fled the restaurant with the two later getting onto a bus where Bankston told the driver to go but the plan hit a snag when Gibbs shot out the tyres.
In response, Bankston began shooting and killing random people before being cornered while using Lee as a human shield while Gibbs aimed his gun at them, reluctant to shoot due to the fact that he was injured which was also affecting his vision.
However upon learning that Amanda was safe, DiNozzo and Ziva having saved the youngster, Lee gave Gibbs the signal to go ahead and shoot them. Gibbs responded by firing several shots, the impact killing Lee but also resulting in Bankston's death as well.
Gibbs later approached Lee's body and felt for a pulse but didn't find one. The next morning, Gibbs who had been treated for his injuries later gave Amanda Lee's NCIS badge.
In a talk, Vance later remarked to Gibbs that death had probably been a good thing for Lee because if she had survived, then it's most likely she would have spent the rest of her life in prison given the overwhelming charges of treason and murder against her.