After NCIS fails to locate a mole in the department, Under Secretary of Defense Corbin Duggan insists on new leadership and takes over the Los Angeles unit from Hetty and Granger.

The team travels to Syria to apprehend a High Value Target where one team member is severely injured when the mission goes awry.

Sam resumes an old alias to bring down a major criminal kingpin; Callen and Anna's romantic night is interrupted when they are tasked with escorting a high-value prisoner to Los Angeles for questioning.

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.