The murder of a petty officer will urge the team to investigate further in the upcoming episode of the CBS long-running series "NCIS."

In season 13's sixth episode titled "Viral," Cartermatt reports that a case involving the death of a petty officer will catch the NCIS' attention. The modus operandi of the murder matches those of a local serial killer. To determine if the culprit is one and the same, the squad must dig deeper in the investigation. Agent Gibbs (Mark Harmon) and the rest can also not rule out a copycat killer. If that is the case, they need to hurry before he can take on another victim.

Meanwhile, McGee (Sean Murray) and Delilah (Margo Harshman) will have to make a big decision that will change their lives in the long run. The agent and his lady love are thinking of moving in together, but they still have a lot to consider before taking the leap. First, they must learn how to compromise. Will the pair be able to work things out?

Last episode, Abby's (Pauley Perrette) rare trip outside her sanctum sanctorum to visit a pharmaceutical lab on a murder case put her in a difficult situation. She got trapped with no communication to the outside world after armed men took over the building and held everyone hostage. Navy Captain Jeremy Doblin, a biochemist, was found murdered. When Abby found a strange compound in his blood, she set out to find its manufacturer.

Her investigation brought her to Celodyne Pharmaceuticals, where she met Dr. Janice Brown (Lucy Davis). Janice told her that the victim was using Celodyne's antidepressants to stabilize his mood, although it obviously did not work for him as he remained cantankerous until death. Before Abby could probe further, however, alarms went off in the lab and armed men came pouring in.

Entertainment Weekly reports that Abby managed to hide in a server room and call Gibbs to tell him what happened. She also locked down the computers to foil the bad guys in case they steal something. The villains, however, knew that an Abby Sciuto was in the building and announced that they would kill her along with the rest of the people inside. When she and Janice got compromised, the NCIS chief forensic scientist threatened that she would release a canister of poison gas.

The culprits refused to call her bluff, so she did it anyway. When Gibbs and the rest got into the lab and apprehended the intruders, they found out that Abby only used a nonlethal incapacitating gas. She then told Gibbs to arrest Janice, as she was the one who masterminded everything. It turned out that she was worried that Celodyne was faking data to sell drugs that do not work, just like in Doblin's case. But one of her cohorts in the lab snapped and killed Doblin when the latter had second thoughts about the heist.

"NCIS" airs Tuesdays at 8 p.m. EST on CBS.