A crime scene poses a national security risk when the LA team discovers the location was used to create a deadly toxin which is now missing.

Kensi connects personally with a discharged Navy Intelligence officer suffering from post traumatic stress disorder who is the sole survivor of a deadly dispute being investigated by the NCIS team.

The team searches for new evidence to prove Kensi Blye’s innocence after she is taken into custody as the lead suspect in a murder investigation involving her deceased father’s sniper unit.

Callen, Sam, Kensi and Deeks spend Christmas aboard an aircraft carrier investigating the death of a fellow NCIS special agent. Meanwhile, Nell and Eric make the most of the holidays back at headquarters and Hetty takes a trip.

In an effort to help Sam and Deeks return to work, Hetty calls upon Operational Psychologist Nate Getz to help them cope with their traumatic experience. Meanwhile, the rest of the NCIS: LA team investigates the murder of a former Navy Admiral and a controversial journalist aboard a private jet.

After an unknown female assailant kills two men disguised as Sherriff’s deputies in front of Callen’s home, the NCIS team gets a new lead in the ongoing mole investigation. Also, Nell visits a prison to interview an inmate withholding information on the department’s leak.