When a young boy finds a murder weapon, the team must trace ownership of the gun to find who used it last and who was murdered.

Dead Marine's day job at a government think tank leads Gibbs and the team into the life of a 12-year-old prodigy who may be the killer's next target.

The NCIS team must determine if the murder of a Navy commander's wife is linked to her profession as a therapist or an act of terrorism after finding the commander's name on a Jihadist target list. Meanwhile, the team discusses Halloween costumes and Tony's recent dating habits.