Callen and Sam are trapped in an armed submarine that terrorists have aimed to hit an aircraft carrier in San Diego. Meanwhile, Hetty defies orders and forgoes her trip to Washington, as the team tries to locate and save Callen and Sam and prevent the terrorist attack.
The NCIS: LA team discovers that one of their own is compromised when they investigate the murder of a Navy contractor involved in illegal transactions of confidential data. Meanwhile, Hetty is under investigation in Washington, D.C., when the Department of Justice arrives in L.A. to investigate the team.
The Department of Justice target a member of the team. Leon delivers unsettling news to Hetty.
The team learns that someone from their past is targeting one of their own. Nate Getz attempts to help Nell get through a traumatic experience.
Callen and Sam make their way to Mexico to locate the only employee who escaped a professional hit at the Department of Defense. Back in America, the rest of the team work to discover the motive behind the shooting.