While on Air Force One, a Navy commanding officer dies. Agents from the Navy NCIS decide to take the investigation into their own hands and also force a Secret Service Agent to help. Now the NCIS team has to figure out if the Navy Officer's death was of natural causes or not.

When a Navy commander's body washes up on shore along with the bodies of two drug runners, Gibbs refuses to believe that the sailor who was killed was dirty.

Gibbs risks his career when his former commanding officer is accused of stealing the funds.

The terrorist from Bette Noir returns with a plan to attack the President. Gibbs and his team follow the clues to reveal his identity and find Kate who is kidnapped.

NCIS discovers that an area in the Marine's bombing range is where mafia has been dumping the bodies for a while. One of the victims is an undercover FBI agent. The team sets out to find a mole.

The team investigates a suicide case, believing that the main reason of her death is a nervous breakdown, but Ducky believes that she was actually murdered. FBI Special Agent Fornell helps them in the investigation. The team discovers that the dead woman was involved in a love triangle and that this may have contributed to her death.

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...

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 bodies of two hired assassins are delivered to the NCIS team, Ziva & Tony go undercover assuming the victim's identities in order to find the person who hired the assassins for their mission. While working on the case, Ziva & Tony spend some quality time in a luxury hotel and the attraction between them arises. Gibbs discovers that his team is not the only one working on the case.

Tony is accused of murdering a woman whos body was found at Quantico and the team must prove his innocence. All the possible evidence prove that Tony is guilty and the team will give their best to set their agent and a friend free.

Gibbs is forced to come back out of his retirement to help Fornell, who is being threatened by a convict that escaped from prison. The convict threatens both Fornell and his daughter Emily. Gibbs and the NCIS team re-open the convict's old robbery case, and question a retired sailor who is the only one who contacted the convict after he was sent to prison. The investigation will lead the NCIS team to a surprising discovery.

When a burnt and mummified body of a missing and wanted person is found on a Marine base, in a furnace, NCIS must work with FBI. The burnt man turns out to be a serial killer. The both teams visit the man's family and discover something shocking. Also, the NCIS team must deal with the book McGee wrote about them, using "fictional" characters.

Director Shepard makes a huge mistake by meeting a man alone to inform her about Le Grenouille, as their meeting turns into a murder of the informant. Now the NCIS team must gather all the existing info and try to finally hunt down their enemy.

When Jenny returns from her European trip, the entire NCIS team will be forced to take a Homeland Security polygraph test, and the deepest secrets of each agent are about to be revealed. Plus, an unarmed Tony and Jeanne are held hostage by a ruthless drug dealer.

When Ducky realizes that one of his cadavers used for research is actually a victim of murder, the NCIS team identifies him as a criminal genius who is capable of deleting the past.

The dead body of La Grenouille finally surfaces and the entire NCIS is put under the investigation by the FBI, with Jenny as the prime suspect for his murder.

Gibbs' hunt for the killer of a marine puts him on a collision course with an old friend.

After a security breach at the SecNav's residence leads to the death of an ICE agent, Gibbs and the team are forced to work with ICE and the FBI to find his killer. Meanwhile, Tony finally comes face-to-face with Michael Rivkin.

When a Marine is found dead, Gibbs, Fornell and the team hit the open road to bust an illegal trucking operation.

When an NCIS polygraph specialist's night job takes a dangerous turn, Gibbs, Fornell and the team have to uncover the truth.

The team investigates a bomb tech's guarded personal life after she is attacked.

NCIS connects a message in blood left by a murdered Navy commander to a manuscript that may contain classified military information.

The NCIS team searches for answers when the current husband of both Gibbs's and Fornell's ex-wife is suspiciously kidnapped.

During a routine stop for his morning coffee, Gibbs finds himself staring down the barrel of a gun, forcing him to question choices he has made in the past and present

With NCIS headquarters damaged by the bomb. Gibbs goes on the hunt for Harper Dearing and to bring him down once and for all.

An explosion at a D.C. event that results in a casualty connected to the agency changes Parsons’ perspective on Gibbs and the NCIS team. Meanwhile, without badges, DiNozzo and McGee investigate the case as civilians, despite the case’s dangerous ties to each of them.

Determined to locate Ziva, Tony chases leads in Israel in search of her current whereabouts. Meanwhile, Gibbs and the team continue the hunt for Parsa and his growing terrorist ring.

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.

When a former NCIS agent's body washes ashore in New Orleans, Gibbs reunites with NCIS Special Agent Dwayne Cassius Pride (Scott Bakula) to determine if the murder was politically motivated or related to a well-known case.

Gibbs and Special Agent Pride chase leads in New Orleans after evidence points to a copycat of the infamous Privileged Killer. Meanwhile, Bishop sends DiNozzo a special souvenir from the Crescent City, as DiNozzo, McGee and the FBI continue to track political connections to the case from D.C.

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.

Gibbs and Senior FBI Agent T.C. Fornell unite after two British prisoners, including a former spy, escape and arrive stateside via a shipping container. Also, McGee is busy apartment hunting and determined to find out how DiNozzo purchased his lavish place.

When a 14-year-old foils a home invasion, Gibbs suspects the teenager is withholding pertinent details. Also, Director Vance and Senior FBI Agent Fornell travel to London as part of the ongoing escaped British spy case.

The NCIS team, alongside the FBI and MI6, continue an international manhunt for an escaped British spy who has left one colleague fighting for their life in ICU.

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

A convicted felon claims NCIS framed him for murder a decade ago, so Gibbs investigates and asks Ducky to conduct a new autopsy. Meanwhile, Senior FBI agent Fornell joins the probe, since he was the lead investigator in the original joint FBI and NCIS case.

After the body of a missing Navy commander is found, Vance orders Gibbs and the team to work with former FBI Agent Tobias "T.C." Fornell, the private investigator who was hired to locate him. Also, Bishop and Torres interview convicted investment advisor Albert Hathaway when the victim is linked to his highly publicized trial.

Former FBI Agent Tobias Fornell pleads with Gibbs to do whatever is necessary to take down drug dealers and suppliers in the area after his daughter, Emily Fornell, is hospitalized from an opiate overdose. Gibbs is haunted by the personal aspects of the case and his history with vigilante justice.

Gibbs and Fornell attempt to track down the leader of a drug ring who supplied drugs to Fornell's daughter. Also, the team deals with the case of a missing cadaver from the NCIS autopsy room.

The discovery of two dead bodies leads the NCIS team into the wild world of modern-day treasure hunting. Also, Gibbs and Fornell get deeper into their search for the opioid kingpin.

Gibbs and Fornell's crusade to find the head of the drug ring responsible for Fornell's daughter Emily's overdose comes to a climax. Also, Gibbs and Vance finally let the team in on a case that has dangerous implications.

While trying to find the serial killer Gibbs was after, the NCIS team discovers another person has been tracking the case as well.

NCIS investigates the apparent suicide of a retired Navy officer who was in Palmer and Knight's grief group; Torres gets a call from NCIS Special Agent Jane Tennant to come to Hawai'i.

The crossover continues on NCIS: Hawai'i S01E18 T'N'T (II).

Following the cliffhanger season 19 finale, with Special Agent Alden Parker still on the run with his ex-wife Vivian, the team investigates who from his past might have a personal vendetta against him in hopes of clearing Parker’s name. Enlisting the help of NCIS: Hawai’i’s Special Agent Jane Tennant and computer specialist Ernie Malick, who are in town meeting with director Leon Vance in preparation for a global military exercise, the group tracks down their prime suspect, The Raven.

The crossover continues on NCIS: Hawai'i S02E01 Prisoners' Dilemma (II).