While an intruder starts to prowl through a home, the resident, a woman Marine, Sergeant Dempsey, who's a bomb-disposal tech, shoots him to death; Gibbs and company investigate; Tony notices an inconsistency, and Abby confirms it. A phone call warns of a bomb aboard a decommissioned destroyer on display at the Navy Yard; Dempsey and others check it out; the bomb explodes and injures her slightly. McGee runs into trouble with a cellphone; Fornell and another member of the FBI become involved. Abby gives the name of the intruder, and the gang discover his background; Gibbs says that he was not a burglar. McGee and Ziva meet Dempsey's brother. Dempsey drops out of sight, but the gang find her on a farm, working with a device and a former drug dealer. Everything works out. Tony almost becomes a poster boy.