NCIS is assigned the case of Paul Booth, a Navy lieutenant who is found with McGee's business card from his days in Norfolk. Booth was a friend of McGee's grandmother, Penelope Langhorne, who developed a research project for the military known as the ANAX Principle before the outbreak of the Vietnam War. The ANAX Principle was then shut down for four decades before being restarted. It uses specially-bred caterpillars to create a genetically-engineered plague. Booth's killer is revealed as Max Ellswood, one of the original researchers of the ANAX Principle, who killed the lieutenant when Booth planned to reveal the program to the press. At the end of the episode McGee and his grandmother speak of how Gibbs reminds them of McGee's father. McGee ultimately decides to call his dad who he hasn't spoken to in seven years.
Meanwhile, Jimmy Palmer struggles with plans for his upcoming wedding.