At an automotive recycling yard the body of a Marine corporal shows up in the trunk of a car; while at the scene Gibbs and the gang see that someone has amputated both feet. Ducky in his shop points out several troubling items, and Tony and Ziva find a troubling cargo inside a truck. Abby goes to Mexico to conduct a class, and McGoo goes to protect her; they take the students outside to do some field work, and several locals interfere; Abby makes several discoveries about an old cold case, and she takes action. Meanwhile Gibbs and the others have figured out who killed the previous victims, but not who killed the last one; then Gibbs finds out who killed the Marine. Abby goes to Gibbs's basement and talks with him from her heart.