A Navy Lieutenant Commander Wade Julius is stripped, face down in the middle of a field by his abandoned car, apparently killed execution style after – the NCIS agents deduce -- a motorist with her car. As agents Gibbs (MARK HARMON), Kate (SASHA ALEXANDER) and Tony (MICHAEL WEATHERLY), and coroner Ducky (DAVID McCALLUM) investigate at the scene in a rural Virginia community, they meet the county’s Sheriff Charlene Dupray, who insists that they will have to share jurisdiction of the crime with her.
First, Gibbs checks out Julius with his commanding officer Dr. Margaret Green, who reveals he was an odd dentist on the Oceana base, and Kate and Tony check out the victim’s home. Meanwhile Abby (PAULEY PERRETTE) performs ballistic tests on the killer’s unusual bullet... and Sheriff Dupray discovers that a similar murder happened two counties over, with the victim also working on the Oceana base. And, oddly enough, there’s DNA evidence from that scene: the murderer relieved himself at roadside.
Just as the agents are corroborating these two murders, an aviator at Oceana, Lieutenant James Seeger, is also found killed in the same manner. While the agents believe this latest one may be a copycat killing, Gibbs interviews Seeger’s RIO and discovers that he and his wife had mutual restraining orders and were about to get a divorce. Further, Seeger was the heir to a fortune from his grandfather’s Swiss Army knife business. Gibbs and Kate then visit Seeger’s wife, Laura. Cool and collected, she agrees to give a DNA sample, but insists she has an alibi for the time of Seeger’s death... which checks out.
Next, Abby ties together ballistics for all three murders, meaning that only one killer is on the loose and effectively voiding the copycat theory. With Laura still the prime suspect, despite her alibi, the agents now deduce that she might have orchestrated these serial killings to veer suspicion away from her true target: James Seeger. She would have only received his inheritance Laura if he died before their divorce was final.
Then, Abby determines that Laura Seeger’s DNA matches that of the roadside killer’s urine evidence sample from the second murder. Still, since Laura’s alibi is ironclad, the agents are in a quandary. Laura directs them to Julius’ CO, Margaret Green, insisting that Green had access to Laura’s urine samples from a physical she recently had. But Green’s alibi for the murders checks out too. Just when their case seems impossible to crack, Kate makes a startling discovery: Laura has a twin sister, which means that the siblings would share DNA. In essence, Laura’s twin killed for her, so that she could receive James’ inheritance.
The agents then descend on Laura’s twin sister – Linda – who was gearing up for her next “serial” killing to continue to keep James’ death inconspicuous.