A lonely, single mother is targeted by a charming conman in an effort to hit an armoured truck carrying millions of dollars. When one of his partners gets killed weeks later, Nichols and Wheeler are on the case.
When an undercover agent is identified and executed by a local gang, the NCIS team must locate the mole before other agents' lives are put in danger. Meanwhile, Granger begins to worry when Kensi disappears in Afghanistan.
When the team investigates a case involving a former marine who is being tracked down by members of al Qaeda for embezzling money from Iraq, Hetty assigns Nell to join Deeks in the field. Meanwhile, Eric is given a new partner in Ops.
When an undercover agent is suspected of working for the smuggler he's supposed to be investigating, the team takes him into custody to find his true intentions. Meanwhile, Kensi and Deeks discuss their personal relationship as Kensi returns to the field.
Sam is convinced that the theft of software for a new unmanned aerial vehicle is connected with the disappearance of the lead engineer's 10-year-old daughter, a girl Sam once provided protection detail for in Saudi Arabia.
When the team and DEA uncover the cartel's plan to slyly transport billions of dollars' worth of cocaine from Columbia to the U.S. using a submarine, Callen and Sam must quickly locate the missing vessel.
The team discovers that one of their own is compromised when they investigate the murder of a navy contractor involved in illegal transactions of confidential data. Meanwhile, Hetty is under investigation in Washington, D.C.
The team takes action to protect one of their own while being interrogated by the Department of Justice. Meanwhile, Nell goes undercover as Hetty, and Director Leon Vance gives Hetty disturbing news while she is in Washington.
When the team learns that someone from their past is targeting one of their own, they desperately search the city. Meanwhile, Operational Psychologist Nate Getz visits Nell to help her through her traumatic experience.
Callen and Sam head to Mexico to track down the only employee who managed to escape a professional shooting at the Department of Defense. Meanwhile, the rest of the team works to uncover the motive behind the shooting.
When a man is murdered by a small drone, the team discovers his connection to a terrorist group that is planning another local attack. With time running short, Nell must use her drone expertise to try to divert a disaster in Long Beach.