After a series of brutal murders, Sergeant Hank Voight and District 21 go after a Colombian drug cartel cleaning house in Chicago, but complicated histories and unit rivalries begin to surface.
The murder of a petty officer sparks a lead in a 40-year-old airport bombing cold case that Gibbs and DiNozzo have been assigned to for the past two years. Also, McGee is jealous that he was not previously briefed on the cold case.
Antonio is sure the Colombian gang is involved in his son's kidnapping and Voight offers him a way to gain information; Halstead discovers some new information about Lindsay.
A Navy lieutenant commander working on foreign cyber threats with the NSA disappears; the team gathers to celebrate the holidays.
The team head to Tijuana after a night of partying ends tragically for an 18-year-old American student. Jack later finds his son working undercover.