Elena and Alaric both lash out at John when Isobel’s unexpected arrival leaves Jenna devastated. Bonnie works with Damon and Jeremy to find the spell they’ll need to harness her ancestors’ power. A heartbroken Caroline doesn’t know what to do about Matt. Stefan and Damon realize they have a new secret weapon.

Still in Chicago, Klaus uses Gloria, a witch he knew long ago, to help him track down missing information that will explain why his plan isn’t working. Gloria’s spells reveal intriguing glimpses of the truth, but she soon realizes she needs Stefan’s knowledge to complete the puzzle. When Stefan suddenly finds himself in danger, help comes from a surprising ally. Back in Mystic Falls, a frustrating new enemy pushes Damon over the brink and he lashes out in a way that will have lasting consequences. Caroline struggles with her own emotional issues, even as she tries to help Elena face her feelings. Jeremy makes a brief but disturbing breakthrough with one of his ghostly visitors, leaving him more confused than ever. Finally, Bonnie has a strange encounter that will affect everyone.

Although Caroline is in no mood to celebrate her 18th birthday, Elena, Bonnie and Matt surprise her with a small party in an unusual location. Damon and Stefan disagree on the best way to handle Klaus , and a reckless Stefan decides to test his theory by taking things to dangerous extremes. Bonnie is concerned when Elena tells her about Jeremy's new plans. At a Founder's meeting, Alaric once again runs into Dr. Fell, who is in the middle of an argument with her ex-boyfriend, the medical examiner. Tyler refuses to go along with Klaus' latest demand, and is surprised when Klaus seems to accept his decision.

Terrifying hallucinations leave Elena shaken and confused, causing her to make a dangerous mistake. After giving Stefan some very disturbing news about Elena, Klaus takes matters into his own hands. Professor Shane reveals a story of ancient witchcraft to Damon and Bonnie. With help from Klaus and Stefan, Jeremy begins a new chapter in his life. Finally, Elena makes a painful personal confession to Stefan, and Matt gives Damon startling new information about Professor Shane.