S5, E16: When Stefan tries to explain recent events to a very sick Elena, her first instinct is to call Damon. At the same time, Damon is trying to figure out how to make a disturbing confession to Elena. While going through Dr. Wes’ files, Caroline discovers a frightening secret, and is surprised when Enzo (recurring guest star Michael Malarkey) appears, claiming to have the solution everyone is searching for. At Enzo’s insistence, Caroline asks Stefan to meet her at a mysterious location where they are joined by a group of Travelers, including Sloan (recurring guest star Caitlin McHugh), who reveals new information on the importance of doppelgangers.