Gone Girl

Nadia is hallucinating from the werewolf bite back to her search for her mother and Katherine reaches out to Wes to try and save her. Stefan and Caroline tell everyone about Katherine being a passenger in Elena's body. Tyler tells them that he bit Nadia so they have to come up with a plan to lure Katherine out, but Katherine figures out they know it's her. For the second time, Bonnie and Jeremy must turn to Liv for help to locate Elena/Katherine. Damon baits Tyler, feeds on him, knocks him out, and takes off to seek revenge on Dr. Wes. Katherine goes to find Wes, but instead finds him dead after Damon killed him. Stefan takes Nadia back to the house and Bonnie comforts her, telling her she'll go to the Other Side, as Katherine comes to say good-bye to her daughter. She gives Nadia a dream about what their life could have been like, had she not been taken away. Katherine tries to run, but she's stabbed and killed with the traveler's knife by Stefan. Caroline and Tyler talk and come to a new understanding. Katherine's spirit goes to Bonnie and reveals she injected herself with a combination of werewolf venom and the ripper virus. She then fails to go to the other side and goes to hell instead.

Plot summary from Wikipedia (CC BY-SA 4.0). Source