A cab driver is slain just hours after he sent an email to an old alias of Callen's.
Four years earlier, Callen spent six months in deep cover as a corrupt military officer, with his goal to get close to three Marines who stole $5 million and collect evidence to convict them.
They convicted all three Marines, two of whom cooperated, however, NCIS didn't find the money because it had been moved.
Even the felons didn't know where.
The murdered cab driver was one of the conspirators, recently released from prison. He emailed Callen, a.k.a. Jason Tedrow, for his help because he thought he found the money.
Kensi interviews the one thief still in prison (he didn't cooperate) and finds herself being interested in his lawyer.
Callen resumes his past undercover role to track down the third conspirator, Jon Donnelly.
Sam isn't pleased to discover Callen had a romantic relationship with Donnelly's sister and she has a four-year-old son (not Callen’s, despite what we are led to believe).
Through the sister, Callen finds Donnelly but he's killed before Callen can speak to him.
They realize the third man in prison must be the connection to missing money and the murders, but when he's also killed, they figure out his lawyer stole the money.