Gibbs and Franks investigate the disappearance of a young Marine connected to a mysterious compound with a charismatic leader, and Lala’s fate is revealed.

When the body of a college swimmer washes up on the beach, the team must determine if it was an accident or murder. Also, Gibbs prepares for his first interrogation.

Young Ducky is sent to Camp Pendleton to shadow the team while they work a case and, in the process, he reconnects with Gibbs after the two crossed paths years earlier.

Tensions rise when Franks’ estranged older brother, Mason, blows into town, desperate for help after hitting rock bottom. Also, the team investigates the robbery of a Navy bank while Lala, still struggling after her accident, makes a decision about her future.

Gibbs and the NIS team investigate the small-town death of a naval officer, but struggle to come up with justice. The crossover continues on NCIS S23E05 Now and Then (II).

When an anonymous tip leads to the discovery of a young Marine’s body at a chilling crime scene, Randy believes it could be connected to a previous case where a coin was left in the victim’s throat. Also, Franks tries to track down priceless packages meant for his brother, Mason.

The team investigates the murder of a Marine who had recently been handpicked for a classified mission. Also, Wheeler’s personal life is upended, Lala is thrown by unexpected news from Vera, and Gibbs and Diane double-date with Randy and his wife.

When Lala’s favorite CI is shot, the team joins forces with Oceanside PD to determine who was behind the attack. Also, Franks visits his brother Mason at the compound, and Gibbs’ relationship with Diane is tested when she gets a job in Los Angeles.

As the team discovers Gibbs’ drunken Vegas elopement with Diane, the newlyweds contemplate their future. Also, the team investigates a fatal movie theater bombing with a connection to the Pruitt compound where Mason is staying.

When a marine captain shows up at Camp Pendleton exhibiting symptoms of a fatal virus, NIS goes on lockdown and Gibbs is forced to take charge. As panic spreads, the team races to determine whether it really is a deadly outbreak or something else entirely.

When a lieutenant’s water-logged body is discovered with a potential connection to an international smuggling ring, NIS Panama agents are called in to assist, and Gibbs comes face-to-face with an old nemesis: Special Agent Dwayne Pride. Once the two are assigned to a dangerous undercover mission together, Gibbs must find a way to move on from their past.

When the NIS Regional Director tries to transfer Mary Jo, she reconnects with an old friend from Atlantic City to help investigate the roadside deaths of two Marines.

When Dr. Tango is arrested for stealing human remains from a national park, Dr. Donald "Ducky" Mallard returns to assist the team in proving his innocence.

When the team's trusted K-9 agent, Gary Callahan, is critically wounded at a crime scene, NIS races to track down the culprit while a surprising pre-Pendleton chapter in Franks' life is revealed.

Lala’s determination to get Manny out of gang life lands the team in the middle of a turf war.

While Gibbs and Lala grow closer on a case, Gibbs’ long-distance relationship with Diane is further tested by the arrival of an unexpected guest.

Wheeler takes command when a car bomb goes off outside NIS headquarters. Also, the truth behind Franks’ distaste for lawyers is revealed.

With the Camp Pendleton office in danger of being shut down, the team confronts an uncertain future.