After Hetty turns in retirement papers and then disappears, Executive Assistant Director Shay Mosley arrives in Los Angeles to oversee the team and immediately makes staffing changes. Also, still mourning the death of his wife and living in a trailer on the beach, Sam is adamant that Callen find a new partner.
During the murder investigation of a Navy Lieutenant on leave in Los Angeles, the NCIS team uncovers classified surveillance briefs she smuggled into the city that may have been sold to a foreign buyer.
When the daughter of a notorious counterfeiter arrives in Los Angeles, Sam is sent undercover as a financier, while Callen partners with Anna to track the family's latest scheme,
After weapons with a million street value are stolen, the team tracks the evidence to a wealthy charity event, prompting Mosley to be added to the guest list with Callen and Sam as her security detail.
Sam goes undercover as a day trader after a prominent investment banker with ties to a Russian oligarch is murdered. Also, one of Callen's aliases is the victim of credit card theft, and Mosley is concerned it signals something bigger.
LAPD Detective Whiting calls in a favor from Deeks after his former partner, LAPD Lieutenant Bates, goes rogue and only Deeks can bring him in.
After an Air Force captain Kensi dated a decade ago breaches a missile launch facility, she is transported to the location to help thwart the use of nuclear weapons.
The NCIS team must locate a group of unknown assailants who illegally crossed the border and attacked California Highway Patrol officers. Also, Homeland Security sends over Specialist Sydney Jones, Nell's older and bossy sister, to assist NCIS with the case.
Callen and the team question CIA Agent Joelle Taylor's backstory after she escapes from a kidnapping and turns to Callen for help.
The NCIS team tracks a highly skilled assailant determined to avenge her father's death by killing a Brazilian diplomat.
The team investigates a ransomware attack that takes out the entire power grid for west L.A. and paralyzes the city. Also, as the first holiday season since the death of Sam's wife approaches, he struggles to find the best way for his family to celebrate.
After napalm is detected at a crime scene, the NCIS team investigates the sole casualty for possible links to terrorism.
While Hetty is being tortured by her captors in Vietnam, Eric and Nell find a clue to her whereabouts, prompting the team to organize a rescue mission with very little information.
Callen, Sam, Kensi and Deeks join Hetty's team from the Vietnam War, Sterling Bridges, A.J. Chegwidden and Charles Langston, in a dangerous and off-the-books rescue mission to save Hetty from her captors in Vietnam. Mosley calls in Nell's sister, a homeland security, to assist the team in Los Angeles with processing evidence connected to Hetty's time in Vietnam.
Callen and Sam pull Granger's daughter, former spy Jennifer Kim, from witness protection to help the team locate an underground spy who has obtained an arsenal of bomb materials.
Callen pursues every alternative when the Diplomatic Security Service apprehends his father, Nikita Aleksandr Reznikov, as part of an exchange for two American photographers being held hostage in Iran.
While investigating a missing person's case, the team uncovers a killer who puts on shows for high-paying voyeurs. Also, Mosley assigns Callen as her partner on a joint ATF mission to apprehend someone from her past.
Callen and Sam join forces with Anna Kolcheck and the Bureau of Alcohol, Tobacco and Firearms (ATF), when Arkady Kolcheck warns NCIS that a notorious international weapons dealer has returned to the states. Also, the case requires Eric to go undercover as a bank IT technician.