The NCIS team investigates a deadly car explosion in D.C. that connects to NCIS Special Agent Nicholas “Nick” Torres, who disappeared six months ago while on a deep undercover assignment in Argentina. Also, Gibbs asks NCIS Special Agent Alexandra “Alex” Quinn to shadow his team after rejecting eight agents she instructed and referred for the open position.

NCIS uncovers a bomb plot and a long-running theft ring while investigating a death at a Quantico reunion. Also Torres and Quinn adjust to life on Gibbs’ team, including new seating arrangements in the squad room.

When the NCIS team investigates a marine sergeant’s tragic fall from a building, her doctor, Grace Confalone, confides in Gibbs and suggests he treat it as a murder investigation. Also, Torres searches for a place to live.

After the body of a navy lieutenant is discovered aboard a destroyer during a tiger cruise, when civilian guests are allowed to spend the night on the ship, Gibbs, Quinn and Palmer travel out to sea to investigate. Also, McGee contemplates the perfect proposal for Delilah Fielding.

When a missing MI6 Officer is linked to a murdered petty officer, Gibbs sends Quinn and Bishop to Philadelphia to work with MI6 Officer Clayton Reeves. Also, Quinn painfully recounts the NCIS case that made her leave field work.

After a kidnapped petty officer escapes her captor, NCIS uncovers a connection to her missing husband. Also, Abby knits the NCIS newbies personalized gifts.

Torres boldly breaks protocol when he learns a witness in an NCIS case is wanted by U.S. Immigration and Customs Enforcement. Also, Abby, Bishop and McGee woo landlord Tony DiNozzo Sr. in the hope of subletting Tony’s apartment.

After NCIS Agent Bishop is sent to Gitmo to gather evidence for a Navy chaplain murder case, she questions her previous work at the NSA. Also, Bishop’s brothers, John and Robert, visit for the Thanksgiving holiday and pester her co-workers to find out who she is dating.

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.

NCIS searches for new leads after an undercover operation to apprehend a businessman who uses acts of terror to manipulate the stock market is compromised. Also, Bishop and Qasim find a break in the case together.

After Gibbs spots the brother of an "NCIS Most Wanted" suspect, he immediately assumes his former alias and goes undercover with their infamous anti-government militia. Also, Bishop and Reeves partner on an off-the-books investigation.

While investigating a hit and run, Palmer spots a man on a ledge and attempts to talk him down.

The murder of a Petty Officer in a small town outside D.C. prompts NCIS to once again work with "The Sherlocks," a privately funded investigative team that includes their newest member, Anthony DiNozzo, Sr.

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. Crossover with NCIS: New Orleans season 3 episode 14.

Bishop is more determined than ever to seek revenge for the murder of Qasim, her late boyfriend, after Gibbs and the team find a new lead in the Chen case. Also, Torres teaches the agents the art of pickpocketing.

McGee discovers his apartment has been torn apart by a robber trying to locate an item of great value hidden somewhere by the convicted criminal who previously owned the unit. Also, Congresswoman Flemming tries to persuade Director Vance to pursue a career in politics.

To carry out a sailor's dying wish, Gibbs and the NCIS team re-investigate a murder case that was originally ruled an accidental death. Also, the case reminds Torres of a tragic time from his past.

When a Marine is murdered at an event for the Honor Flight Network, a non-profit that arranges for veterans to visit the World War II, Korea and Vietnam War Memorials for free, the NCIS team must rely on an irritable Vietnam War veteran, Henry Rogers, to provide details on the victim’s whereabouts throughout the day. Also, McGee and Bishop investigate a juicy rumor about Quinn and Torres.

After a vice admiral’s laptop is infected with ransomware, he enlists McGee and the NCIS team to track down the hacker before the computer virus eliminates his personal and professional files. Also, Alex takes time off to assist her mother, Marie Quinn, after she receives a “911” text.

Torres must rely on old case notes and contacts after a Marine’s murder is linked to a former dirt bike gang he joined for a year-long undercover operation.

After a Marine Sergeant is found murdered in a National Park, Gibbs and the NCIS team partner with Mounted Police Sergeant May Dawson to solve a string of related crimes in the park.

The stress of McGee and Delilah’s imminent wedding takes its toll, as Delilah is rushed to the hospital. Also, the NCIS team travels out to sea after a young and healthy Petty Officer aboard a Navy destroyer dies in his sleep.

Gibbs, McGee and Torres travel to a remote area in Paraguay, controlled by a group of violent rebels, in an attempt to locate a missing Navy SEAL who disappeared during an unsanctioned trip.