Elena comes home to a nightmare; Damon realizes Katherine has returned; Tyler receives a surprise visit from his uncle.

When a confused and desperate Caroline leaves the hospital and joins her friends at the Mystic Falls Carnival, Damon wants to take immediate action.

Elena, Damon and Alaric go to Duke University to find Isobel's research into the paranormal and look for clues to the mystery surrounding the Lockwood family; Stefan faces a new danger in the woods; Tyler makes a shocking discovery about Mason.

Katherine recalls the past.

Tyler learns more about the Lockwood family curse from Mason, and Sheriff Forbes receives startling information.

Katherine chooses a new victim. Bonnie discovers new information about Mason and shares it with Stefan.

Elena decides to take matters into her own hands and offers a tempting incentive to Rose for her help. When things take an unexpected turn, however, Rose calls on Damon to deal with the plan Elena has set in motion. Jeremy's reckless attempt to help Bonnie retrieve the moonstone lands him in a life-threatening position and forces Stefan to put himself in danger. Bonnie and Luka form a closer connection. Tyler shows Caroline the Lockwood cellar, where she makes a discovery that leaves them both terrified.

As the full moon nears, Caroline helps Tyler prepare for his transformation. Meanwhile, Damon and Alaric are suspicious when a stranger shows up looking for Mason.

Elena meets Stefan at the high school and he tells that he is watching her following Klaus's order. Rebekah, who is staying at the Salvatore's house, is in the same class as Elena. Elena plots with Alaric and Damon to lock Stefan in the dungeon of the Salvatore house. Tyler is fascinated and reveling in his sire bond to Klaus. Vicki convinces Matt to bring her back from the dead. Anna tells to Jeremy that darkness is surrounding Vicki, and that she has made a pact with the Original Witch. Vicki hits Matt on the head and seeks out Elena as part of her agreement with the witch. Meanwhile, Damon stays with Rebekah while Elena and Alaric abduct Stefan. Katherine awakens Mikael who confesses that he does not drink human blood, he instead feeds on vampires.

On the day of the Night of the Illumination in Mystic Falls, Mason ties Damon to a chair and the vampire believes that it is a prank of his brother Stephan. Later Mason tells that he is seeking redemption and wants to destroy Klaus to help Tyler. He goes with Damon to a cave with tunnels where it is supposed to have a weapon to destroy the Original Vampire. Elena asks Jeremy whether he may contact Lexi to learn how she can bring humanity back to Stephan, but her brother explains that he has no connection with Lexi. Bonnie goes with Caroline to the place where the witches were burnt and she casts a spell from the Grimoire to bring the dead back. Her grandmother Sheila returns and tells that she must close the passage, destroying the necklace, since the Original Witch is sending every ghost that still has pending business back to Mystic Falls. Meanwhile, the vampires from the tomb also return seeking revenge. Lexi contacts Elena and she starts Stephan's "treatment". Caroline does not find the necklace on the place that Damon told her that it would be and she suspects that Anna has stolen it. Damon can not go ahead through the tunnel that is protected and Mason goes alone. Anna returns the necklace to Jeremy and Bonnie casts a spell; Lexi, Mason, Anna and her mother, the vampires from the tomb and Sheila vanishes.