As NCIS mourns the loss of Ducky, the agents find comfort in working on one of his unfinished cases involving a woman whose father was dishonorably discharged from the Marines.

NCIS, the FBI, and MI6 continue an international manhunt for an escaped British spy who is targeting current and former agents.

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.

As the hunt for Ziva's replacement begins, Gibbs and his remaining team members must head back to work with the past still weighing heavily on their minds.

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.

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

The team tries to verify the identity of Joe Smith, who claims he served on the U.S.S. Arizona during the attack on Pearl Harbor, and wants to be buried there upon his death.

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

A group of serial terrorists seek revenge and send Ari 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.

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.

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.

NCIS comes under attack by a mysterious enemy from the past.

Still stressed over Kate's death, Gibbs is even more hurt when Ari kidnaps Ducky and decides to play with his mind. Gibbs sends Tony to follow Ziva, and after Jenny and Gibbs are almost shot to death, he is even more determined to finish once and for all with Ari, and Ziva's strange connection to Ari will be just the help that he needs.

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.

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

While the NCIS team investigates the link between a dead journalist and a Petty Officer, Ziva is taken aback by the sudden emotional visit by her father, who she hasn't seen in more than two years.

The NCIS team investigates whether a fire on a U.S. Navy ship that served as a secret detention site for indicted terrorists was accidental or an intentional diversion for an escape.

The NCIS team investigates copy-cat crime scenes while Gibbs navigates two ex-wives relentlessly trying to get his attention.

The NCIS team re-examines an ambush on a group of Special Ops snipers in Iraq after an American couple is attacked in the same area six months later.

Gibbs must face the consequences of helping Ziva with "the one thing" she said she'd take care of before returning to her family.

After the terrorist's attack, the NCIS team is shocked and is trying to cope with Kate's sudden death, each in their own way. Now, their mission is to collect all the possible info on Ari and find a way to stop him before he does any more damage.

The NCIS team must work on an assignment against a terrorist group without Gibbs, who is still recovering from the explosion. Gibbs has to fight with memory loss, while he's visited by his mentor and his former boss. His help is needed, especially when the team discovers that Gibbs is the only person who has information about the terrorists' plans.

When a Navy Lieutenant becomes the victim of radiation poisoning, the NCIS team must find the person who's behind the crime. The Lieutenant, who is working for the International Atomic Energy Agency, claims that only his two colleagues knew about his assignment, and whoever it was, the person tried to stop the Lieutenant's next investigation.