While trying to track down a delusional and violent Marine who thinks he's still in Iraq, the NCIS team will learn that the man has been the subject of a secret experiment - and it comes with a high price to pay.

Gibbs and his team are searching for a cyber serial killer who takes videos of his victims. The team quickly finds out that the video's of the dead victims are false.

A murder prompts the reopening of one of Tony's old investigations, leading Gibbs and DiNozzo to reverse roles to solve the case.

The body of the son of a retired Colonel-turned-preacher is found and the team have their suspicions that he may be the victim of a hate crime. Meanwhile, Gibbs gets a holiday visit from his father.

Gibbs is worried about Tony's ability to handle his job when Tony's father turns out to be linked to their newest investigation, an assassination attempt on a foreign prince.

The team hopes to avoid an international incident when an American officer is killed on a British ship.

The team is surprised when Gibbs asks Tony's father to join them in a murder investigation.

A petty officer's recruitment session at a college fair comes to a fatal end, prompting the NCIS team, accompanied by Dr. Mallard's predecessor, to solve his murder.

The line between McGee's personal and professional life is blurred when NCIS uncovers a connection between his grandmother and the murder of a Navy Lieutenant.

After Anthony DiNozzo, Sr. is found in a car with a dead body in the trunk and no memory of the previous night, the NCIS team must figure out if he is capable of murder. Meanwhile, Tony is sidelined for this case and must go against orders to try and prove his father’s innocence.

Following the murder of a Marine, Tony and Ziva join Ziva’s longtime friend and mentor in Columbia in a search for a missing Marine Lieutenant and Navy Chaplain. Meanwhile, Jimmy Palmer decides who will be his best man.

A petty officer is gunned down in a billionaire’s Ferrari and the investigation leads the NCIS team to discover a link to a man Gibbs was named after.

Gibbs teams up with FBI Agent Fornell on a joint NCIS/FBI investigation after Fornell becomes the target of a shooting, but they face an unexpected twist in the case when their mutual ex-wife, Diane Sterling, gets involved. Meanwhile, rumors run wild among the group after Diane stays overnight at McGee’s.

In the aftermath of an event that strikes close to home, the NCIS team unites to seek answers and demand justice in order to protect their most vulnerable colleagues.

While the team takes a missing persons case, Tony is disturbed by Ziva's way of coping with her father's death.

DiNozzo returns to his Baltimore Police Department days when he sees a felony suspect from a 15-year-old case at the NCIS crime scene of a murdered Petty Officer.

Complications arise when the NCIS team discovers a link between a murder victim and the current boyfriend of Gibbs and Agent Fornell’s ex-wife. Meanwhile, NSA Analyst Ellie Bishop adjusts to joining the NCIS team.

After a bomb detonates in the dressing room at a military charity concert, the NCIS team must determine if the target was a washed-up ‘80s rocker or if the bomb was part of a larger scheme. Meanwhile, Jimmy prepares for fatherhood

After a Navy officer is found dead on a rural road, the NCIS team must ascertain if the murder was the result of a bar fight or because he knew too much about an attack on a fellow female officer. Meanwhile, DiNozzo and McGee start a juice cleanse to purge their bodies of impurities.

During a joint Coast Guard and NCIS training exercise at sea, Gibbs and CGIS Agent Borin spot a deceased man overboard, who is discovered to be a missing crew member from a ship 60 nautical miles away. Upon boarding the ship for questioning, Gibbs finds himself on a vessel that has been commandeered by pirates.

The Secretary of Defense calls on NCIS to help a sailor who is battling leukemia to locate a donor for a bone marrow transplant, after two of his siblings are killed in the line of duty. Meanwhile, Bishop returns home to Oklahoma for Thanksgiving.

The NCIS team investigates a series of escalating threats against congresswoman Jenna Flemming, while Director Vance oversees her temporary protection detail.

After the NCIS team tracks evidence from the murder of a Navy captain to Ducky’s deceased mother, Ducky looks back and questions a pivotal life choice he made 37 years ago. Also, the team exchanges holiday gifts, and Gibbs spends Christmas dinner with Fornell.

After Abby's homeland security think tank is compromised and she is found in possession of a real bomb, the NCIS team discovers the leader of the group has been murdered and a theoretical terror playbook has been stolen.

The crossover continues on NCIS: New Orleans S03E14 Pandora's Box (II).