When an antiterrorism device is stolen, the team must quickly find the suspect and the device before an attack is made against Los Angeles. Meanwhile, Hetty realizes the case is bringing her back to someone from her past.
Callen and Sam enlist the help of a Gurkha, an elite Nepali soldier specializing in knife fighting, to retrieve a missing thumb drive. Meanwhile, Kensi and Deeks struggle to find a balance in their partnership.
Sam and Callen head to Mexico to search for Tuhon, a retired assassin they encountered on their very first case together. Meanwhile, Nate and Deeks stay in Los Angeles to assist with the investigation.
Following an explosion at a fish market, the team partners with an undercover DEA agent to determine if the incident is an act of terrorism or a botched drug smuggling deal. Meanwhile, in Afghanistan, Granger and Kensi investigate a helicopter crash.
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.