Mary's latest witness is a smooth-talking con man, who finds it impossible to leave behind his life of swindling other people even while in the witness protection program. But despite discovering that he has failed to leave his old ways behind, Mary is even more frustrated to learn that his inside connections to a major weapons trafficker make it impossible for the federal government to drop him from WITSEC -- and instead requires that she and Marshall go undercover with him to try to catch the weapons dealer.