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 takes action to protect one of their own while being interrogated by the Department of Justice. Meanwhile, Nell goes undercover as Hetty, and Director Leon Vance gives Hetty disturbing news while she is in Washington.