The team must find assailants who illegally crossed the border and attacked California Highway Patrol officers; Homeland Security sends Nell's older and bossy sister to assist with the case.

Callen, Sam, Kensi and Deeks join Hetty’s team from the Vietnam War, Sterling Bridges, A.J. Chegwidden and Charles Langston, in a dangerous and off-the-books rescue mission to save Hetty from her captors in Vietnam. Also, Mosley calls in Nell’s sister, homeland security specialist Sydney Jones, to assist the team in Los Angeles with processing evidence connected to Hetty’s time in Vietnam.

Sydney turns to her sister Nell for help after her high school crush, Andre Martinez, is mixed up in a Russian plot to steal intelligence from the Department of Defense. Also, Special Prosecutor John Rogers conducts mandatory performance reviews with the team.