Season 9 begins with Hetty turning in retirement papers and disappearing. A new executive director arrives and immediately makes staffing changes. Meanwhile, Sam, still mourning his wife’s death, insists 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.

After weapons with a $1 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. Meanwhile, 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 when Deeks' former partner goes rogue.

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

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.

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. 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.

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.

After a cryptocurrency farm is robbed of over $10 million in Bitcoin codes, Sam and Hidoko go undercover, with Sam resuming a likely compromised former alias.

Callen, Sam and Nell must find pieces of a failed rocket launch, including a top-secret government device; Hetty tries to help Keane acclimate to life in the states.

NCIS partners with the FBI after a Marine is murdered by a rare nerve gas. Also, Deeks shares his dream to quit law enforcement and open a bar.

NCIS investigates the murder of a federal prison inmate who was the adopted daughter of a notorious counterfeiter. Also, Callen is summoned by the Alcohol, Tobacco and Firearms (ATF) Internal Affairs board to discuss Anna Kolcheck’s actions during a joint NCIS and ATF case.

After Sam is shot during a firefight with the cartel, a suspect is interrogated and reveals new information on the whereabouts of Spencer Williams, the man who kidnapped Mosley's son five years ago.

Despite several team members having grave reservations, NCIS travels to Mexico for a risky mission to locate and rescue Mosley's son.