CGIS Agent Abigail Borin and a Coast Guard ship come across a yacht with two murder victims. A third person, a Navy admiral's daughter, is missing. Borin teams up with the NCIS team to find out what happened to the victims, who were studying the effects of climate change in the Gulf of Mexico. The missing woman left behind a young toddler, who is in the care of the admiral.
Many of the victims' possessions are missing, and it looks like they were the victims of a robbery at sea. They figure out that a man named Clive is the thief. When they track him down, he says the two murder victims were already dead by the time he boarded their boat.
Patton Plame recovers a brief portion of video from the incident, and it looks like Anna Huntley, the admiral's daughter, may have been involved with the deaths and disappeared on purpose. The team talks to the faculty advisor, Dr. Sandra Jones, who indicates that there may have been a love triangle and that Anna had money problems.
Sebastian manages to narrow the search area, but instead of Anna, the searchers find rare Spanish silver coins. Treasure hunting may have been a motive for murder.
Plame locates a man named Merris, who is looting the area for the pesos, and he gives up his competition, a woman with the screenname SunkenTreasure14. The team is shocked to discover that she's actually Dr. Jones, who was bitter about the lack of pay in her line of academia.
The victims had caught her diving in the restricted preserve area to retrieve the pesos. When they refused to split the profits, things got out of hand and all three of them were shot.
With Dr. Jones's direction, search teams recover Anna Huntley's body.
Meanwhile, LaSalle deals with his bipolar brother Cade, who has been hiding from everyone for five years. Despite some tension, Cade tentatively accepts LaSalle's overtures.