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.

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.

Season 15 begins with the NCIS team tirelessly searching for Gibbs and McGee two months after they were last seen fighting an elusive group of rebels in a Paraguay jungle. Meanwhile, Vance and Torres are summoned to a congressional hearing regarding the fallout from the Paraguay mission.

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

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.

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.

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.

As Vance prepares to host diplomatic talks with Venezuela, the team is called in to investigate the dead body of one of his inside men.

NCIS is called in to investigate when a lieutenant returns home on the eve of Halloween to find a surprise party being thrown for someone else at his place.

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

NCIS investigates when the body of a murdered Navy lieutenant, who disappeared over a year ago, is found by a cemetery grounds crew while relocating caskets on the property. Meanwhile, Gibbs and McGee must pass a psych evaluation before they can officially resume working.

NCIS comes under attack by a mysterious enemy from the past. Also, Vance tries to mend fences with his estranged son by explaining why, despite the ongoing dangers of his job, he still chooses to stay at NCIS.

While the NCIS team investigates the link to a dead journalist and a Navy petty officer, Ziva is taken aback by the sudden emotional visit by her father, who she hasn't seen in more than two years. While Ziva questions the purpose of her father's visit as the Director of Mossad, her father insists he is in the U.S. strictly to see his daughter for Shabbat dinner.

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

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.

When an infamous arms dealer, Reymundo Diaz, is released from prison and bodies start piling up, Torres is forced to face the repercussions of his actions during an undercover operation he worked on years ago.

NCIS investigates the unexpected death of a Navy reservist who was an investigative journalist. Also, Knight and Jimmy’s budding romance is put on hold when a vital organ transfer goes fatally wrong.