Jeremy is delighted to have Bonnie restored to her powers, yet worried when accompanying her and Damon to the house where a 100 witches were burned to gather enough power to undo the moonstone's curse. Elena's mother Isobel Flemming's return startles her and even Katherine, as turns out doing Klaus's bidding for a gruesome 'prize'. John Gilbert confesses more wrong choices, also at Jenna's expense, yet unlike furious Alaric, Elena ends up choosing to keep her father in her life. The Salvatore brothers piece together from the Gilbert diaries what they believe equals a secret weapon. Matt can't handle the vampire truth and gets Caroline to wipe his memory.
After the arrival of Isobel, Jenna decides to leave Elena's house. Meanwhile Jeremy and Damon go with Bonnie to the house where Emily Bennet and one hundred witches have burnt to death to collect their power. Jeremy discovers that Bonnie has hidden the truth about the power she has acquired. Katherine steals the moonstone and Isobel abducts Alaric, betraying Elena, Damon and Stefan. Matt betrays Caroline with his mother. John finds that he has been lured by Isobel.
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.
- Isobel (Mia Kirshner) shows up on Jenna's doorstep. She refers to Jenna (Sara Canning) as the woman who's dating her husband. Isobel asks to come in, but Elena (Nina Dobrev) tells Jenna not to invite her in. She slams the door in Isboel's face.
Jenna is crushed when she realizes Ric (Matthew Davis), Elena and John (David Anders) all knew Isobel was still alive.
The Salvatore boys react to the news. Katherine (Nina Dobrev) doesn't think they should tell Isboel she's in town. She's reconsidering her alliance with her.
Ric comes to Jenna's. She won't talk to him, she's going to stay on campus. She asks Elena to pick up the Lockwood's check for her mom's foundation.
John strolls in and suggests they let her go. She tells Ric he should have been more honest with her. Ric decks him and leaves.
Caroline (Candice King) talks to Stefan (Paul Wesley) about Matt (Zach Roerig). She doesn't know where he is and hasn't been able to give him vervane.
John asks Elena and Stefan to come downstairs. Isobel is there. He says she has info on Klaus. She says rumors of the doppelganger are out. John says killing the 1864 tomb vampires was a way to protect Elena since they're the only ones who knew where she was. She's still bitter they nearly killed Stefan and Damon (Ian Somerhalder) in the process.
Isobel wants Elena to go to a safehouse in her name where vampires can't reach her. She refuses.
Bonnie (Kat Graham), Damon and Jeremy (Steven R. McQueen) go to Jonah's apartment to look for info on the Salem witch burning ground. Bonnie says Jonah gave her a message- she could use that power if she finds the spot. "Great, we'll put that on our list of things to do today: Harness ancient dead witch power," Damon says.
Bonnie magically scans the stacks of books to find the one they need.
Isboel returns home, but is quickly jumped by Katherine. Katherine grabs her around the neck, but then they laugh and hug like old pals. Isobel says she's been busy making a deal with Klaus to save Katherine's life.
Isobel confesses she went to Jenna's because she was jealous. She tells Katherine that John has been useful because he thinks she's trying to protect Elena. Isobel hasn't been able to find Klaus, but she did get close to one of his witches. Klaus will release Katherine if they bring him the moonstone and the doppelganger. Katherine says she can get the moonstone. Katherine says she was willing to go along with the boys' plan, but they're floundering.
Back at the house, Katherine asks where the moonstone is. Damon isn't sharing.
Caroline looks for Matt at the Lockwood function but comes up empty.
Damon takes Jeremy and Bonnie to the place Emily Bennett and the other witches burned. It's an old run down mansion.
Inside, Damon walks around the house and suddenly can't move. The sun starts to burn him. His ring isn't working. Bonnie says she doesn't think the witches like him being there.
Back at the house, Katherine goes through the boys' things looking for the moonstone. She finds cash and pockets it. She checks the chimney and gets dirty. She goes to wash her hands, and then she sees it -- sitting with the soap.
Isobel finds Ric in town. She says she wants to apologize. She says she compelled him to let her go. She says she loved him. Then she lets her witch friend have at him and Ric crumples to the ground.
Damon waits outside the witch house. When he tries to go in, the door slams in his face.
Bonnie prepares to read from the book of spells. They hear the spirits of the witches who died there.
Bonnie listens, but tells Jeremy she can't understand.
At the Lockwood's function, Elena accepts the check to the Miranda Gilbert scholarship fund. Isobel walks up on John in the upstairs stairway. She tells him she's creating a distraction, then chomps on his neck. Moments later, he tumbles down the stairs and everyone runs toward him, including Stefan. Elena is left alone. Katherine steps out and grabs her.
Stefan goes back to find Elena.
Meanwhile, Isobel drives off with Elena in the back of her car. Stefan follows Katherine outside but quickly figures out who she is. She injects him with something, saying she can't have him following her.
At the house, Bonnie screams in pain as the witches' voices get louder. Jeremy tries to reach her but is knocked back. After a while, she stops, and says she did it.
At the Lockwood house, everyone has cleared out. Damon arrives. Carol and the sheriff (Marguerite MacIntyre) think he's dead. Damon explains about his ring and says John will be fine.
Liz goes outside and finds a very angry Matt waiting for her. He wants to see his sister's Vicki's file, and accuses her of covering up that Vicki was killed by a vampire.
Damon brings John home and dumps him. Stefan calls and tells him what happened.
Isobel calls Katherine, who is at her house. Elena is awake to hear Isobel tell Katherine "he" wanted the moonstone and her. Katherine turns around to see Maddox (Gino Anthony Pesi), and he immediately makes her fall screaming to the floor.
Caroline leaves Matt another voice mail. Then she looks in her house to see him waiting for her. Her mom brought him there. He says he didn't tell the sheriff about Caroline. Matt recoils from Caroline. He wants to know more.
Outside the witch house, Bonnie says the witches' chant was a warning to be careful with the power. She demonstrates, turning the sky black, bringing thunder and swirling leaves all around.
Damon and Stefan go to Isobel's house. They look around, find nothing and leave.
Isobel brings Elena to a graveyard. She shows Elena her tombstone.
The man who incapacitated Katherine tells Isobel her part is finished. he can let Elena go. He says she did what Klaus compelled her to, but she's done. Isobel apologizes for being a disappointment. Then she rips her protective amulet off her neck and quickly burns to death in the sunshine, right in front of her tombstone and her daughter.
Back at her house, Caroline tells Matt everything, including she loves him. He says he's all alone because his sister's dead and all of his friend's are liars. He says he doesn't want to know everything. She asks what she can do. He asks her to make him forget. He demands it. Crying, she agrees.
Back at the house, Elena can't help feeling a tiny bit bad about Isobel being dead. She doesn't understand why they let her go.
Damon suggests it's time to formulate a plan. He gives Elena the deed to his house to sign into her name, so she'll be safe from vampires.
John wakes up and quickly finds Damon's hand on his throat. John insists he had no idea what Isobel was planning. Elena suggests they talk.
Jeremy reads over the spell book. The warning says if all of the powers are used, it could kill the witch. Bonnie says killing an original would take all of the power. He says he won't allow it. She says there's a reason she has these powers. She says if she's the only one who can stop everything, it's her decision to make.
Matt gets in a car and confesses. He tells the driver he drank the vervane, got Caroline to confess and then asked her to take it away. We see he's talking to her mom. She thanks him for telling her what happened. She asks what Caroline says. Matt says he feels like Caroline died, and her mom says she did.
John tells Elena he didn't realize Isobel and Katherine were genuinely friends and working together. John says he believed Isobel because he saw how heartbroken she was to give Elena up, and he loved her. He says he'll do whatever Elena wants, including leave.
Elena tells him he screws everything up, but since he's the only parent she has left, she can try to learn not to hate him.
Damon tells Stefan that Bonnie got the powers. They realize they're the only ones who know about her. "That literally makes Bonnie our secret weapon," Damon says.
Katherine wakes up to see the man who knocked her out chanting over a man as he's drained of blood. We pan around and see it's Ric. He rips the IV out of his wrist and stands up, triumphant. He says hello to Katherine -- with an accent. It's Klaus.