Callen and Sam find themselves trapped inside an armed submarine that terrorists are intending to use to hit an aircraft carrier in San Diego. Hetty goes against orders and forgoes her trip to Washington, as the team attempt to locate and save Callen and Sam and stop the terrorist attack.
The NCIS: LA team find out that one of their own has been compromised as they investigate the murder of a Navy contractor involved in illegal transactions of confidential data.
The Department of Justice target a member of the team. Leon delivers unsettling news to Hetty.
The team learns that someone from their past is targeting one of their own. Nate Getz attempts to help Nell get through a traumatic experience.
Callen and Sam make their way to Mexico to locate the only employee who escaped a professional hit at the Department of Defense. Back in America, the rest of the team work to discover the motive behind the shooting.
Sam is arrested accused of murdering a woman and Callen and Granger attempt to clear his name.
A man is murdered by a small drone, so the team suspect a terrorist group is responsible. Nell attempts avoiding disaster at Long Beach.
After Deeks and Kensi work under cover to investigate the murder of a homeless man they discover a connection to a Mexican cartel.
Eric is one of seven suspects after Granger is poisoned by the mole.
The team become involved in an investigation into the murders of Marines whose sons are at military academics.