A KILLER VIRUS — 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 (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 (guest star Caitlin McHugh), who reveals new information on the importance of doppelgangers. During spring break on a mostly deserted Whitmore campus, Elena runs into Luke (guest star Chris Brochu), a student who seems to know her, though she has no memory of meeting him. Recently dumped by his boyfriend, Luke proposes that he and Elena spend the break getting drunk together, but she sends him off on an urgent mission to find Bonnie and the “newbie” witch, Liv (guest star Penelope Mitchell). Damon finally tells Elena the truth about his recent activities, and they come to a new agreement about their relationship.
— OFFICIAL SYNOPSIS FOR THE VAMPIRE DIARIES: WHILE YOU WERE SLEEPING (EP516)
MARKOS ARRIVES IN MYSTIC FALLS — In order to keep Stefan from being harmed by Sloan (guest star Caitlin McHugh) and the Travelers, Caroline and Enzo (guest star Michael Malarkey) agree to make a trip to Atlanta to find a newly discovered doppleganger [sic]. Caroline is surprised when Enzo opens up to her about his past. Damon and Elena spend an awkward afternoon at Jeremy’s parent-teacher conference, where they hear bad news about his behavior at school. Afterwards, Damon reluctantly tells Elena upsetting news about Jeremy’s personal life. Bonnie has an unsettling encounter with Luke (guest star Chris Brochu), and learns more about his family history. Liv (guest star Penelope Mitchell) fills Jeremy in on the rumors about the Travelers’ next move and demonstrates her considerable power. Jeremy makes an unexpected deal with Liv, then makes a decision that is devastating to Elena. Stefan and Caroline share a special moment of friendship. Finally, a terrifying turn of events at the Travelers’ camp leads to the appearance of their mysterious leader, Markos (guest star Raffi Barsoumian).
— OFFICIAL SYNOPSIS FOR THE VAMPIRE DIARIES: RESCUE ME (EP517)