Vance, using members of the Gibbs team, in Chicago works the case of the murder of a man who, Vance insists, was once a member of the Marine Corps. Gibbs wonders whether Vance has exceeded his authority. Later Vance hears what happened.

Two runners at the US Naval Academy find an unattended car and the body of a civilian physician; Gibbs and company investigate; Vance recognizes the MO of a North Korean woman assassin. The gang find the pieces, and everything works out.

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.

A human ear in the Potomac River leads to the rest of the body, wearing a uniform of a Navy petty officer; Gibbs and company investigate. Ziva's father shows up, as does his Iranian counterpart. Gunfire interrupts a dinner. [Continued.]

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.

Tony and Ziva, with only minor injuries, return to work; the others find the getaway car and the body of the wheelman, which provides a clue; Ilan contacts Ziva; Tony interprets the lead, then Ziva pursues it and draws the case to an end.

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.