A bomb explodes in the apartment of a Navy lieutenant (junior grade), Keith, while he's not at home; the building manager dies; Gibbs and company investigate. Keith washed out of flight training and now serves at the Pentagon. Gibbs talks with Keith's CO; Abby says that Keith built the bomb. McGoo has a problem, but Vance takes care of it in two different ways. Vera, a retiring agent and an interesting person, works her last two weeks with the Gibbs gang. Tony and Vera check out the source of the explosive, who refers them to a local contractor, who reacts in a squirrelly way, but who reveals an important fact. Abby identifies a plastic blob; Tony and McGee elaborate; Tony traces Keith to an airport. Everyone shifts into overdrive to find Keith; McGeek proposes a technique, and Abby helps to implement it; soon the team and others track Keith in a rented private light aircraft. Gibbs speaks with Keith, who changes his plan and ends his flight.