NCIS is called in to investigate an explosion onboard an offshore oil platform that resulted in the death of a Marine. Abby finds hidden malware installed on the operating mainframe of the oil platform which enabled a hacker to manipulate the systems. The team questions the woman who originally designed the program, Danielle Benton, but they reach a dead end. Gibbs and Special Agent Abigail Borin investigate the platform to find remnants of the detonator. The placement of the detonator on the bridge of the platform leads them to believe the bomber had intimate knowledge of the platform’s structural layout and only targeted that specific section. When they discover that the firm who designed the plans for the oil platform previously experienced a security breach from the same type of malware found on the mainframe, Benton becomes the prime suspect. After the team tracks Benton down, she explains that she stole the designs in order to stage an onboard protest of offshore drilling and was not responsible for the bombing. Soon after, Abby uncovers pieces of a select leather briefcase brand from the victim’s body and traces it to Brett Creevy, a lawyer from the oil company last seen lamenting the fallout from the explosion. They confront Creevy and he confesses to profiting from short-selling shares of the company’s stock before the explosion but did not know the victim was on the bridge of the platform at the time of the bombing. Meanwhile, the team questions the agenda of SecNav Porter and wonders who is behind the sophisticated Halloween pranks in the office. Gibbs helps Borin come to terms with the death of a loved one in combat.