Gibbs and McGee head to Alaska while the team works at home to uncover the conspiracy behind the serial killer.

After Ducky is attacked by a man claiming to have information about his half-brother who died decades ago, the NCIS team searches for the perpetrator, as Ducky recalls the final emotional days he had with his sibling. Also, with the holidays approaching, Bishop and Jake discuss the future of their relationship.

During an NCIS hit-and-run investigation, Palmer joins a stranger on the outside ledge of a building in an attempt to save his life.

After a malnourished and confused 9-year-old is found hiding in a storage unit, NCIS reopens an old missing persons case when the girl is believed to be the daughter of a Navy recruit who disappeared 10 years ago. Also, Bishop discovers notes that Special Agent Ziva David kept on the case long after NCIS officially stopped investigating.

Flashbacks reveal the murder case that first introduced young Gibbs to NCIS and his introduction to young, new-to-America Ducky.

Ernie Yost, an elder Marine veteran confesses to murdering his best friends almost 60 years ago in a war battle and the NCIS's job is to solve all the secrets and save Ernie from prison.

One month after Director Vance was kidnapped, Gibbs is assigned the role of acting director in his absence while the team searches worldwide for his whereabouts.

While investigating the death of an intruder at Quantico, Jimmy and Kasie are exposed to a deadly biotoxin; the NCIS team calls on Dr. Carol Wilson for help as they race to find the antidote; Torres tries to distract Jimmy's daughter.

Parker’s delinquent past resurfaces when NCIS is called to Philadelphia to investigate the death of a Navy petty officer.

A gruesome mishap at a Navy petty officer’s gender-reveal party leads NCIS to the case of a missing teacher that was popularized on a true crime podcast.

When the NCIS team engages in Walk-a-Mile day to gain a new perspectives on different departments, things take a turn when Kasie receives a distress call from a mysterious man.

When Tony opens a mysterious letter thinking it's for him, a small puff of white powder comes out and it releases a possible deadly virus. Kate calls for help and soon she and Tony are isolated in a bio-hazard isolation room for precausion. McGee and Gibbs work to discover who sent the envelope and how to cure their friends before its too late for them. Meanwhile, Tony's health gets worse...

A group of serial terrorists seek revenge and send Ari (guest star Rudolf Martin) on an assignment to kill Gibbs. The NCIS team goes on a hunt after him, but when they discover that Ari has a bigger plan, it is already too late... the NCIS team will have to face the death of one of their team members...

Gibbs finds himself emotionally challenged when he agrees to investigate a crime connected to a friend of his daughter, who passed away years ago, and the investigation leads to a shocking conclusion.

When a murder investigation leads the team to Gibbs' hometown, secrets about his past are revealed.

Terrorism shakes the foundations of the Navy and NCIS to such an extent that Gibbs and the team face surprises that will devastate them.

After NCIS finds a secret government bank account that’s funding a nationwide network of vigilante justice, the team must determine who is acting as judge and jury.

After Torres and Bishop are victims of a hit-and-run, Torres fights for his life in the Intensive Care Unit.

When one of their own is killed, the team must find the killer before they get to another member of the team, Gibbs. In an emotional investigation, the team tries to stay together, against the wishes of Assistant Director Vance.

Torres relies on his team's investigative skills after he wakes up on a dilapidated fishing boat and is covered in blood and unable to remember the last 12 hours.

NCIS investigates the death of a man on a cruise ship whose body is discovered in the ship's sauna by none other than McGee's mother-in-law, Judy.

NCIS investigates the case of a Navy reservist whose body is found in a beat-up car at the end of a gun range. Kasie weighs the pros and cons of buying a gun.

NCIS is called in when Navy Chief Warrant Officer Rafi Nazar is suspected of trying to sell stolen classified Navy software used to pilot combat drones.

After a civilian research vessel in the North Atlantic picks up a small boat of wounded Navy officers, NCIS arrives on the ship and is forced to hide after discovering terrorists on board. Also, Agent Knight takes a paper doll with her on the mission to capture photos for her niece’s grade school class.

When the body of a Navy lieutenant is discovered missing an eye, the NCIS investigation leads to the world of cage fighting.