While on liberty in Baltimore, Maryland, a boatswain's mate second-class dies of a stab wound; Gibbs and company investigate; the prime suspect is a brother-in-law of Vance. The team persist, Abby solves the case, and they nab the bad guy.

Gibbs and company continue to investigate the killings at Vance's home, seeking whoever hired the shooter; the gang identify the hit man and later figure out who's responsible. Ziva buries her father, and Vance and the team bury Jackie.

A lance corporal collapses and dies on an obstacle course at the MCB, Quantico, Virginia; Gibbs and company investigate; Ducky sees many wounds. Another injured Marine dies. The team figure it out. Vance finds and solves personal business.

Within 30 miles of Washington, DC, eight kids in Navy and Marine Corps families have suddenly become badly ill, requiring treatment in ERs and ICUs; Gibbs and company investigate; Carol, of the Naval Medical-research Center, joins the effort; immediately the number of sick kids grows to 14, then 19, 23, 28, and 34, and none of them responds to treatment. Duckie announces the first fatality, who was a veteran of Vietnam, then he describes the cause of death and the treatability in the kids. Abby says that she has misidentified the particular nature of the illness, so she, Jimmy, and Carol keep working, and they eventually nail it. Abby gives Jimmy a lecture about kindness, optimism, and parenthood. Then the gang identify an international traveler who in many places has recently encountered many kids and the fatality. Meanwhile Vance has three tense chats with his estranged father-in-law and then a nicer one.

A Navy Commander is murdered near the White House, it is learned that he was on his way to talk to the President. Gibbs and his team must determine if it is because of his relationship with the President or because of his marital problems.