Using a high-definition satellite to survey the Virginia coast, a CIA analyst inadvertently witnesses a murder. While taking his satellite off his actual target and – instead -- watching a nude sunbather in a restricted area of the Little Creek Naval Amphibious base, he sees a man get stabbed, but can’t make out the killer. He anonymously reports the murder, and Gibbs (MARK HARMON), Kate (SASHA ALEXANDER), Tony (MICHAEL WEATHERLY) and Ducky (DAVID McCALLUM) arrive at the crime scene on the naval base shoreline. They find Lieutenant Commander Thomas Egan, in a wet suit and a knife in his back. Then visiting his workplace, Gibbs and Kate talk to his commander, Lauren Tyler, as well as a civilian, Jonathan Overmeyer. Overmeyer runs Side Scan, a company working with the Navy on base to develop high-tech, classified sonar equipment. Soon, the agents learn that Egan was involved in the development of an advanced sonar device designed to conduct surveillance through sound waves. Egan had gone to the site where he was murdered to test the equipment, and Abby (PAULEY PERRETTE) finds that – scouring his computer files – he had been having misgivings about its imminent introduction. Since the device is not recovered on the site, it offers no immediate clues to Egan’s murder. Gibbs and Kate also visit Egan’s upset wife Trish, also a Navy Lt. Commander, who says he revealed his work to her strictly on a need-to-know basis.
While Ducky conducts an autopsy, Tony tries tracking down the anonymous caller. His efforts lead the team to deduce that the call came from within the CIA. Gibbs has initial difficulties procuring information from the agency to determine which employee matches the phone number. So, he enlists Abby’s help in contacting a colleague of hers at NASA, Ashton Kugel, who – using his own technology – can pinpoint the satellite’s operator, down to the CIA office the call came from. Gibbs and Kate then find their man: 23-year-old satellite analyst Jeremy Wirth who admits to seeing the murder committed. With Jeremy’s admission, Gibbs finally gets help from the CIA in procuring the satellite-recorded images of the murder. Meanwhile, Ducky deduces that the murderer is left-handed.
Looking for more clues, Gibbs then interrogates Lauren Tyler further, learning that she and Egan were having an affair. She further reveals that testing of the sonar device wasn’t going well. A missing prototype would give Side Scan and Jonathan Overmeyer more time to work out kinks in the equipment, so that he wouldn’t lose the Navy contract to make the device. That finding puts Overmeyer squarely in NCIS’ suspect realm as well, particularly as he is left-handed.
Sorting through the satellite images that Jeremy recorded, the team does get a close-up of the nude sunbather, and Tony succeeds in locating and interviewing her on base. While she didn’t witness a murder, she did covertly see a woman arrive at the scene to speak with Egan. That would point to Lauren as a suspect, but she is right-handed. So, Gibbs then looks to another possible motive. Since Egan was having an affair, the murderer could possibly be his wife. Gibbs realizes that, by taking the sonar device after she committed the killing and – in essence -- pointing the investigation in that direction, Trish Egan could believe she was getting away with murder. So Gibbs and Kate then visit her to see if they can test their theory and set a scheme in motion. They tell Trish that they believe that her husband was seemingly killed for the sonar device. If they could recover it, they could catch his killer.
Asking for Ashton’s help with his satellite to track Trish into a remote wooded area, Gibbs, Kate and Tony arrive to find her recovering the sonar device she had hidden... proving her guilt in Egan’s death.