Borderland

After finding a dead Marine with his feet cut off, as well as a truck full of dismembered feet, the team begins to believe that a serial killer is loose. Meanwhile, Abby is invited to provide a forensic science lecture in Mexico by Alejandro Rivera, and McGee goes along as an escort. While there, Abby is tasked to solve a cold case involving the murder of a drug dealer 20 years ago, and Abby eventually finds out the drug dealer was the one murdered by Gibbs. Back in the United States, the team deduces that the Marine was the killer, acting as a hit man to kill rival drug dealers and kept their feet as proof. One of the drug dealers is apprehended and she admits that she killed him in self defense. Finally, Abby confronts Gibbs about the murder, which Gibbs admits to. They both agree that somebody is trying to dig up Gibbs' past, but Abby is conflicted on whether to drop the case or pursue it and asks Gibbs whether he will love her regardless of what she does.