Nell reports that, in Tijuana, Mexico, local police, aided by USA forces, have gunned down the kingpin of the Barbosa drug cartel; however, by bizarre means the body of the victim disappears from the morgue as soon as it arrives; the Sec Nav directs Callen and company to investigate the possibility of a leak on the US side and to find the missing body.
Meanwhile, Eric and Nell get festive for the holidays, Hetty takes a trip; and Deeks gets jealous when a marine lieutenant is attracted to Kensi.
A former defendant of Deeks is targeted for discovering information that could dismantle a lucrative car shipping operation with links to an Asian terrorist ring.
Meanwhile, Hetty summons Operational Psychologist Nate Getz to be her "pawn" and the rest of the team sense another evaluation on the horizon.
It was later determined that a member of the coroner office that NCIS worked with had been supplying bodies to a funeral home owner for use in body parts trafficking.
The team investigates the death of a former member of a domestic terrorist group called "Gun Barrel Party", a group that was wanted for a string of bombings and domestic terrorism during the 1970s, leading them to discover a connection between a member of a current anarchist group "Red Tide" and the "Gun Barrel Party" that could lead to another bombing.
Callen is concerned that Sam might be too invested after he takes on a missing persons case to help find the nephew of an Afghani elder who helped him years ago when he was wounded on a mission in Afghanistan while the boat shed becomes an unlikely battleground when the supposedly missing nephew arrives along with a terrorist on the NCIS Wanted List, a terrorist who also wants Sam dead, forcing Callen, Kensi, and Deeks into an intense gunfight before it's too late.NCIS: Los Angeles is a drama about the high-stakes world of a division of NCIS that is charged with apprehending dangerous and elusive criminals, who pose a threat to the nation's security.By assuming false identities and utilizing the most advanced technology, this team of highly trained agents goes deep undercover, putting their lives on the line in the field to bring down their targets.Callen and Sam team up with NCIS Red Team after a Marine is killed execution-style in Moscow, Idaho.In the process, the joint investigation also uncovers a terrorist plot similar to that of September 11.When one soldier dies and another one is treated in hospital for cyanide poisoning after drinking water out of the same jug, the team investigate whether it was an isolated incident or a test for large scale water contamination.