After bombing at a party that kills the SECNAV, DOD Inspector Parsons starts to believe in Gibbs and helps him find who is trying to kills the NCIS team. Tim is seeing a woman named Delilah who provides information about the bomb.
A Navy lieutenant illegally buys explosives and plans to blow up the ship where he was assigned. He rents a plane and loads it for a suicide mission. The team asks a music band to use their twitter account to locate the plane.
A woman impersonating a soldier is killed. She was an Afghanistan woman smuggled into the states by Mike Franks. Gibbs & McGee travel to Afghanistan to find the person who leaked the woman's identity to the killer and to rescue more women.
When the team investigates the death of a sailor outside Baltimore, Tony sees a former police informant he thought was dead. The former informant was wanted for a crime which seems to be connected to the sailor's death.
The NCIS team works with Abby Borin from the Coast Guard to solve a death that occurred during an explosion on a ship. They must find the person who caused the explosion and murder. In preparation for Halloween, someone plays pranks at NCIS.
A soldier is killed in a store, seemingly just another death in a string of robberies. Tony & Tim solve find the soldier was targeted. Gibbs and his father visit a dying man who was in the war at the same time as Jackson, one who saved him.
The NCIS team is forced to re-examine a hit-and-run murder case when a former FBI agent turned lawyer confides in Gibbs that her client's confidential alibi is solid. Meanwhile, McGee grows suspicious of Tony's strange behavior.
Someone gave a bugged ink pen to the SecNav to overhear classified information. The team finds this scenario was described by an NSA analyst two years ago, so they have the analyst, Ellie Bishop, help track the traitor. Ellie joins NCIS.
Diane Sterling ex-wife of Special Agent Gibbs and FBI Agent Tobias Fornell surfaces as the NCIS team discover a link between a murder victim and her boyfriend. NSA Analyst Bishop continues to adapt to her joint duty at Anacostia.
After a mysterious illness strikes children from military families, Gibbs and the team investigate the cause. Meanwhile, Abby and Jimmy partner with the Naval Medical Research Center to determine the strain of illness, all in hopes of delivering a cure before the holidays. Also, Director Vance struggles with forgiveness as his estranged father-in-law makes a surprise visit to his home. Meredith Eaton and Ben Vereen guest star.
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.