Damon insists on Katherine to reveal her plans to him. She tells him that she has the necklace, and she has Jeremy. Pearl once told Katherine she knew how to kill Klaus, but she didn't share the information with her, only with Anna. Bonnie accidentally lets is slip to Katherine that Vicki and Anna have been communicating with Jeremy from beyond the grave. Anna never had the intentions to help Katherine, but Katherine threatens to hurt Jeremy so Anna gives in. The only person that can kill Klaus is Michael. The problem is that he is entombed and if they let him out, he'll kill everyone since he kills vampires.
Klaus realizes that the original witch had lied to him saying he had to kill the doppelganger - he now knows he has to keep Elena alive. Hybrids needs doppelganger blood to complete their transition. He tests this on Tyler and feeds off his blood.
Klaus compels Stefan to feed on Elena. He tries to resist but ends up giving in, sending Elena to the hospital. Klaus goes and siphons her blood to create more hybrids. Damon comes to stop Klaus. Damon says "Michael", which is enough to send Klaus running. Damon takes Elena home and offers to compel her to forget everything that's happened. She refuses, insisting that everything she's experienced is importnat to remember.