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.

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.

When a stolen drone is linked to the elusive terrorist Parsa, the NCIS team partners with the Department of Defense, including Gibb’s former girlfriend Hollis Mann, to track down the device before it is used for a large scale attack. Meanwhile, McGee hesitates to ask for time off to attend a black-tie gala honoring his girlfriend.

In an effort to find the terrorist Parsa, Gibbs and the NCIS team track down one of his cohorts using evidence from the drone attack. Meanwhile, an emotionally shaken McGee struggles with the ramifications of the incident.

After uncovering faulty bulletproof vests in a truck filled with stolen U.S.M.C. merchandise, the NCIS team attempts to locate both the source and any vests that had been shipped to military personnel overseas.

After returning to her job at the Department of Defense, McGee’s girlfriend Delilah finds a break in a controversial case, prompting her to turn to the NCIS team for help. Meanwhile, McGee talks to DiNozzo about whether he should ask Delilah to move in.

When a petty officer’s murder matches the M.O. of a local serial killer, the NCIS team must determine if this is the killer’s latest victim or the work of a copycat. Also, McGee and Delilah must learn to compromise before moving in together.

The NCIS agents’ personal plans are interrupted when each of them catches errors in a seemingly cut-and-dried closed case. Also, McGee and Delilah argue over the importance of not discussing work during dinner, while DiNozzo bores his date with shop talk.

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.

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.

The team suspects foul play when a healthy, young petty officer mysteriously dies in his sleep aboard a Navy destroyer. Wedding stress reaches its peak for McGee and his fiancée.

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.

McGee reluctantly visits his high school after the unique computer password he used as a teenager is linked to the murder of a department of defense contractor. The case escalates when an intruder breaks into McGee’s home in an attempt to steal his archaic high school computer.

McGee and his wife Delilah's (Margo Harshman) Bahamian vacation turns into a high-stakes mission when a case NCIS is tracking of a dead escape room manager has ties to the island. Also, Gibbs fears the worst when his search for Fornell leads to blood.

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.

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 death of a college student who was killed while running across the street and had connections to McGee’s wife, Delilah.

After discovering the remains of a Marine captain, the NCIS team travels to Texas to interrogate the suspected killer.