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. Also, Mosley calls in Nell’s sister, homeland security specialist Sydney Jones, to assist the team in Los Angeles with processing evidence connected to Hetty’s time in Vietnam.

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.

After napalm is detected at a crime scene, the NCIS team investigates the sole casualty for possible links to terrorism.

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.

The NCIS team tracks a highly skilled assailant determined to avenge her father's death by killing a Brazilian diplomat.

Callen and the team question CIA Agent Joelle Taylor's backstory after she escapes from a kidnapping and turns to Callen for help.

The team must find assailants who illegally crossed the border and attacked California Highway Patrol officers; Homeland Security sends Nell's older and bossy sister to assist with the case.

Kensi is transported to a missile launch facility to help thwart a takeover of nuclear weapons.

LAPD Detective Whiting calls in a favor when Deeks' former partner goes rogue.

Sam goes undercover as a day trader after a prominent investment banker with ties to a Russian oligarch is murdered. Meanwhile, one of Callen’s aliases is the victim of credit card theft, and Mosley is concerned it signals something bigger.