The episode starts with Damon handing a stressed-looking Caroline a glass of blood to comfort her. Stefan arrives and asks them what happened. Caroline tells the Salvatore brothers that she was confronted by Katherine at the Mystic Grill. There is a flashback to when Caroline got to the Grill. She runs into the bathroom after an embarrassing encounter with Matt. In the bathroom. Katherine suddenly appears behind her. Caroline pretends to think it's Elena, and Katherine pretends to be her at first and asks her if she is OK. Caroline plays along for a bit, until she runs to the door in vampire speed to escape, but Katherine anticipated it and was able to block her. She asks her to deliver a message to them and says: "Tell Damon and Stefan that I want the moonstone, or I will rip this town apart until it rains blood." She then instructs her that the deal is to go down that evening at the Masquerade Ball. Damon assumes that she got scared, noting that what she did to Jenna in the previous episode was desperate. Stefan states that they can't underestimate her. Caroline suggests giving Katherine the moonstone, but Damon says "No, Katherine isn't getting dick!" and explains that he's going to kill Katherine at the ball. Stefan interrupts, saying that Damon wouldn't be killing Katherine because he was going to do it himself.

Meanwhile, Matt, Elena and Jeremy are bringing Jenna home from the hospital. It is revealed that Jenna was told that she ran into a knife while making dinner, even though in reality, Katherine had compelled her to stab herself earlier. Jenna  is embarrassed about it, but they all soothe her by telling her it was a freak accident. While Jenna is resting, Jeremy and Elena are alone together and he asks his sister what they are going to do about Katherine. Elena says they're not going to do anything. She believes that Katherine hurt Jenna because she was still with Stefan and now that they're broken up, they're safe. Jeremy tells Elena she is being naive and walks away.

Katherine returns to her room at Mrs Flowers' Bed and Breakfast, and she helps her get comfortable by bringing her shopping bags. When she leaves, Katherine starts to take a dress out of one of the bags when Suddenly, a woman (a witch named Lucy) slinks into the room. Katherine hears her and runs to her in super speed and presses her against the wall, scolding her to not to sneak up on a vampire. Lucy replies: "Don't attack a witch! .. It's good to see you, girl." They hug. Lucy says that she came because she asked her. "Like you had a choice," says Katherine. She tells Lucy about the Masquerade Ball and asks her to come with her and she smiles. 

Caroline opens the door of the Salvatores' house and Bonnie comes inside,holding the Grimoire in her hands. Alaric and Damon are seen in the background looking at weapons. Jeremy is also there and tells Bonnie: "We're gonna kill Katherine", when she asks what everyone is doing. Bonnie gives them a puzzled look, to which Stefan says "Let me explain...okay, we're going to kill Katherine.". Bonnie looks shocked. Stefan walks over to Damon and Alaric, the latter of whom is explaining how to use each weapon. Cut to Katherine straightening her hair and talking to Lucy in a snide tone: "I'm impersonating my dull-as-dishwater doppelgänger Elena. She has the worst taste." Katherine says she's gotten quite good at pretending to be Elena. She says she wants the moonstone and that she wants Lucy to help her. When she asks her what she wants to do with it, Katherine doesn't answer. "You want me to break the curse," assumes Lucy. "Let's just get it first," Katherine says, "What I really need is for a backup. I can't imagine that Damon and Stefan are just gonna hand it over without putting up a fight."

Bonnie tells Stefan that their plan is risky. Stefan clarifies that it's about more than wanting Elena back, that what Katherine did to Jenna crossed the line and that she needs to be stopped before it happens again. Bonnie is still not quite convinced, but reluctantly says she could do a spell to trap Katherine, similar to the tomb spell. Meanwhile, Elena is at her house with Matt. She tells him that Alaric will be coming over to spend time with Jenna . She invites Matt to join them, but he tells her that he's going to the Masquerade Ball. Elena responds that she's not going because of what's going on between her and Stefan. Matt tells her that he's going because there's something he has to do, but won't go into detail. She looks suspicious, but tells him to go and have fun. When Matt brings up Stefan, Elena says she doesn't think they're going to get back together: "There is so much about me and Stefan that will never work." Matt says that he's always here for her and they hug.

At the Salvatores' house are Alaric, Stefan, Damon, Jeremy, Caroline and Bonnie, getting ready to go through with their plan. Alaric asks if they're sure that they don't need his help at the ball, but Stefan says: "No. I need you to stay with Elena, I don't want her to know about this." Alaric promises he'll look after her. When Stefan asks if anyone wants to back out, no one wants to. Caroline states that Katherine killed her and that fair is fair, but it takes Bonnie longer to reply; in the end, she says she is in as long as nobody gets hurt (except Katherine, anyway).

At the Masquerade Ball at the Lockwood Mansion, artists are seen doing tricks with fire and people in masks are watching. Inside in the office, Tyler is getting ready. His mother, Carol, tells him it's already packed outside. Mother and son compliment each other on their looks. Tyler apologizes for his past behavior and asks his mother about Mason. She says she hasn't heard from him and doesn't think she will. Carol mentions that the Masquerade theme was her late husband's idea. She says that they both loved him and that "it's natural to feel abandoned. I just don't want you to feel alone." They decide to go outside and pretend to have some fun.

Katherine and Lucy arrive in masks. She runs into Matt and he thinks it's Elena. Katherine compliments him in his suit. She compels him, saying: "Do you know what you have to do?" Matt answers: "I'm going to get Tyler Lockwood really drunk. I'm going to start a fight with him and beat him until he snaps." "And then?", asks Katherine. "I won't stop until he kills me," says Matt. Katherine then asks him to leave.

Stefan is outside looking around when Damon comes to him from inside the mansion. Neither brother has seen Katherine yet. They play mind games on each other about loving Katherine and whether one of them will or will not hesitate to kill her. Sarah and Aimee are inside the office dancing with each other, and Matt and Tyler are there too, drinking and talking. Tyler says he likes that for once, it's Matt corrupting him, and not the other way around. "OK, let's go party," says Aimee and Sarah and the guys follow her. Jeremy is seen going upstairs with a bag in his hand, followed by Bonnie. They enter a room, which Bonnie exclaims is perfect for what they need to do. Jeremy opens the bag and they take out weapons and Emily Bennett's Grimoire . Bonnie explains the spell to Jeremy. When he asks her about her magic, she explains that she doesn't want to know too much, and that she's only practiced spells that do good. She then admits that she doesn't really like any of this supernatural drama and doesn't really want to be a part of all of this. When Jeremy says being a witch must be cool, Bonnie says it's anything but that because of what she knows about what happened to her witch ancestors: "It never ends well for people like me." She says she only helps because she doesn't want anyone else to get hurt and that she doesn't know how to stay out of it.

Jenna and Elena are at home eating pizza. Jenna says she feels like an invalid. When Elena asks her aunt where Jeremy went, she says that he went to the Lockwood party, which surprises Elena. Jenna says that she's glad he's having some fun. Elena, suspicious, pretends to go get napkins, but actually goes into the kitchen to talk to Alaric. She tells him that she feels like everyone is avoiding her and wants to know what's going on. Alaric says that he can't tell her anything, but when Elena suggests that maybe she should go to the ball after all, he clearly has a problem with it. He tries to deflect by telling her that he's supposed to keep an eye on her in case Katherine shows up and tries to hurt her while everyone else is at the party, but she just gets more confused and upset, saying that Stefan would never go to any of the Mystic Falls events by himself, because he only attended them for her. Alaric tells her to drop it, and she appears to go along with it,

Jeremy and Bonnie go to tell Stefan that the room is ready, but on their way, Bonnie gets a strange feeling and walks over to Lucy to ask if they know each other. Lucy deflects by saying that she's a plus one and knows no one, and quickly takes her leave. "Are you OK?" asks Jeremy and Bonnie answers: "Just got a weird vibe. Let's find Damon."Outside, Stefan is seen, still looking around, until he finally eyes Katherine and walks towards her a little. Suddenly, she shows up behind him and asks him to dance with her. Stefan refuses, and Katherine asks him to choose someone at the party for her to kill instead. Stefan finally agrees to dance with her. Katherine tells Stefan she didn't expect Jenna to survive, acting innocent, asking: "How does one stab oneself?" Stefan tells her he doesn't want anyone to get hurt tonight. Katherine agrees and says: "Just give me the moonstone." He tells her that he doesn't have it on him, and tells him they would have to get it together. Katherine, who expected this, simply says "Or, you can go get it by yourself and bring it here, and I will try not to kill anyone while you're gone." Stefan then says: "My way or you don't get it." They are interrupted by Aimee Bradley, asking Stefan where Matt is. When she sees "Elena", she compliments her and her dress. Katherine thanks her and tells her she loves her necklace. She says it's twisted, pretends to go fix it, but instead cracks her spine, paralyzing her from the waist down, followed by another crack that kills her. Then she says: "The moonstone, Stefan. Tick tock!" and leaves, leaving dead Aimee in Stefan's arms to deal with.

Back at the Gilbert house, Elena tells Jenna and Alaric she's going to bed, but she instead grabs a key and sneaks out the door to go to the Lockwoods'. Stefan tells Damon that he left the body in the trunk for now. Damon says they'll dump it later and writes it off as collateral damage. Stefan says that this is why they just need to call the whole thing off, but Damon convinces him to change his mind again, saying: "What? Who's hesitating now? Hey! Don't do this to me. This woman ruined our lives, she destroyed us. Tonight it ends. We can do it together. I got your back. Alright?" Stefan reluctantly agrees.

Jeremy and Bonnie are outside and Jeremy asks her random questions. "Can you do a hocus pocus to pass a math exam?" "I don't know that spell." "Huh. That would be the first one I'd learn. Or a sex spell or something, I don't know." He asks her to dance while they are waiting, and Bonnie says "No!", like it is a crazy idea. Jeremy chuckles and plays it off well, and Bonnie says: "I mean... no, thank you." Jeremy's phone rings. He received a message from Damon, saying: "Now." They look at each other and Jeremy stands up.

Lucy catches up with Katherine, saying: "You didn't tell me there was another witch here." Katherine plays dumb, but Lucy says that no one was supposed to know that she was involved in this. Katherine says she owes her dear friend - meaning herself - a favor. Jeremy appears, pretending to think that Katherine is Elena. He asks Lucy to let him talk to his sister alone and she leaves. He drops the act and tells her that Stefan and Damon want to meet her at the edge of the lake by the woods and that they brought the moonstone. She asks him why he's doing the Salvatores' bidding, and he responds that he's not afraid of her. She jokes that the Gilbert men are so courageous and reminds him how she cut off John Gilbert's fingers. She finally leaves, and Jeremy is texting when suddenly Elena pulls him behind a bush. She asks him: "What the hell is going on?"

Caroline sees Matt laughing and drinking with Sarah. Tyler appears and wants Matt to go somewhere with him, when Matt sees Caroline. They smile at each other for a moment, but Matt leaves. She receives a message from Jeremy saying: "Your turn." She goes into another room. Katherine appears and presses her to the wall, throttling her. She asks her what Stefan and Damon are up to, and Caroline purposely pretends not to know anything. She finally admits that they're trying to kill her. When Katherine asks for the moonstone, Caroline tells her that Bonnie has it and also tells her - after another bit more throttling - that she's upstairs.

Elena is shocked to find out that they want to kill Katherine here. She tells Jeremy and Bonnie that they're crazy and that they'll get themselves killed, especially Jeremy, who she doesn't want to be involved in this sort of thing in the first place. Bonnie says they know what they're doing, and Jeremy explains that they saw an opportunity and had to take it; he also adds that Katherine went after Jenna and needs to be stopped, and that he's involved regardless of whether he wants to be or not.

Caroline is whining while Katherine pulls her upstairs with her. She tells her in which room Bonnie is, and Katherine walks into it, asking: "Where is she?" She turns around and sees Caroline smiling before saying: "I did it. I didn't think I'd be able to fool... you, but... I did it." Katherine tries to run towards her, but is being held back by the trapping spell Bonnie cast earlier. Stefan appears in the room, and Caroline leaves. She taunts Stefan, asking him if he really thinks that he can kill her with the stake in his hand, and he just smiles and says no before adding "But he can." as Damon comes out of the closet and shoots a stake out of a crossbow into her back.

As the stake impales Katherine, Elena is seen screaming outside, with a blooming red bloodstain on the back of her shirt. Damon stakes Katherine in the deltoids, and Elena screams in pain again, blood blossoming from the same spot in the same arm. Everywhere Katherine gets hurt, Elena feels the same pain and gets the same wounds. Bonnie finally realizes that the doppelgängers are linked to each other and yells at Jeremy to run and stop them before they kill Elena on accident. Katherine, Stefan and Damon continue fighting, and when Damon is just about to drive the stake through Katherine's heart, Jeremy appears and yells: "Stop! You're hurting Elena! Everything you're doing to her is hurting Elena." Damon looks confused and shocked and looks at him, his arm frozen in mid-air. She gets up and says: "You think you two were the only ones with a witch on your side? Wrong. Something tells me that my witch is better than your witch." Stefan tells Jeremy to check on Elena and he leaves. "Let's all make sure poor Elena's OK," Katherine mocks, and starts to cut her palm with the stake just to hurt Elena even more. Katherine is about to stake herself in the stomach when Stefan stops her. Bonnie tells Elena that she can't undo the linking spell, but that she can do a spell to take some of the pain away. Jeremy comes back to Bonnie and Elena and tells them Katherine had a witch on her side. Bonnie realizes it's Lucy, the mystery woman she got the vibe from, and runs away to find her. Jeremy offers to give Elena his Gilbert Ring in case they try to kill Elena through Katherine, but Elena prefers to know that Jeremy is safe.

Katherine reminisces about the old times in 1864 to the Salvatores, making snide comments about what a bore Damon was back then and how much of an inconvenience his obsession with her was. Stefan asks Katherine why she was working with a werewolf (Mason). Damon tells him not to waste his breath, mockingly apologizes about killing Mason and Katherine explains that Mason isn't the only wolf in town.

Sarah asks Matt and Tyler what happened to Aimee, and the boys don't know. Matt purposely spills alcohol all over the floor of the office and over a picture of his deceased father. Tyler asks Matt what's wrong with him. He gets Tyler mad by saying mean things about his father and bringing up the times that his dad beat him, and breaks the frame of the picture. Even though Tyler says: "I'm not gonna fight you", Matt makes the first move and they start fighting anyway, Matt because he is compelled to, and Tyler in  order to defend himself.

Caroline walks through a room, still smiling about her achievement, when she hears Tyler and Matt fighting in the office. She runs into the room, asking what's going on. She pulls Matt far away from Tyler. When Matt still won't stop, Caroline elbows him in the face and knocks him unconscious. Tyler looks at her, shocked about her strength. She immediately sees if Matt is OK. Meanwhile, Sarah grabs a knife, muttering: "If Matt fails, I can't." Caroline sees her coming and starts to warn Tyler, but it's too late; Sara stabs him in the clavicular area with a knife, and he instinctively pushes her away. She falls backwards, and her head hits the edge of the desk and cracks her neck, dying immediately. Tyler is shocked and doesn't know what to do when Sarah doesn't wake up. Caroline checks her pulse and realizes she's dead. Tyler freaks out, starts screaming in pain, and his eyes change colors, signifying the werewolf curse being triggered.

Damon, Stefan and Katherine are still waiting for Katherine's witch, Lucy. Stefan realizes something. He remembers that she told him that she gave George Lockwood something that he needed to make him help her fake her death. He figures it's the moonstone. He wants to know why she needs it back but Katherine just changes the topic and says: "I love you in a suit. So dashing." Meanwhile, Stefan figures the moonstone wasn't hers to begin with and asks who she was running from in 1864 when she faked her death. She changes the topic again, saying that in 1987, while Stefan was in a concert with Lexi, she was there to see him. Stefan asks her again who she was running from, and she just whispers: "I love you."

Bonnie finds Lucy. She walks away when she sees her, but Bonnie follows her. She tells her her first name and says: "I should've known I'd run into a Bennett." Bonnie wants to know how she knows her. She says she doesn't want to fight her and that she will stop the spell that links Elena to Katherine if she gives her the moonstone. Lucy finally tells her about Katherine: "The bitch saved my life. And now I owe her." She's about to leave, when Bonnie grabs her arm. Lucy senses that Bonnie has the moonstone on her. "Can you feel that?" she then says, "You can trust me. Give it to me. It's OK."

Upstairs, Damon is about to kill Katherine with a stake, but Stefan holds him back. Damon says: "The second the spell's lifted, I'm gonna drive a stake right through your heart." Katherine isn't scared,  just says: "God, you're hot." Lucy appears and gets their attention. She has the moonstone in her hand and tells her that the spell is broken and that she can leave. "When I hand this over, my dept to you is over," says Lucy. "I owe you nothing." Katherine agrees and she gives it to her. Then suddenly Katherine starts gasping and falls. "You should've told me another witch was involved," says Lucy. She also says that Elena is fine and that the spell is broken and explains that with Bonnie with her, she will heal quickly. She apologizes for her involvement to the Salvatores and leaves.

Caroline explains a different version of how Sarah died to Carol. After she leaves, she tells Tyler that Matt is in the car sleeping it off. Tyler asks her why she is covering for him. He says she doesn't know what it means, that Sarah's dead. Caroline says she does but Tyler shakes his head. She asks if his wound has healed and he asks: "How did you...?"

Lucy is walking away from the house and Bonnie asks her to wait. She apologizes and makes it pretty clear that she is not more of a fan of vampires than Bonnie is. She asks Lucy how she could know she could trust her, and Lucy responds by asking her if she's ever felt that feeling before. Bonnie says that she has felt it before around family, and her Grams. Lucy says that they're cousins. She says seeing her was a wake-up call, that she had to stop letting vampires control her. She thanks her and leaves. Bonnie asks her to wait again, saying she has so many questions and that she doesn't want to be in the middle of all of this either and asks her how to stay out of it. Lucy says: "Unlike me, you're one of the good ones, Bonnie. The middle of it is exactly where you need to be." She tells her to take care and that they'll see each other again and finally leaves. Bonnie looks after her. Jeremy walks over to her, saying he's going home and offers her a ride. She sees her face and asks if she's OK. She nods, giggles, and asks him when he got his driver's license. Jeremy laughs and tells him he's not a kid anymore. She says she'd love a ride home.

Stefan sees Elena outside. She promises she will see a doctor about the wounds but assures him that she's OK. She asks if Katherine is really gone. Stefan nods. They smile at each other. Stefan says he was so worried and comes closer to her, but Elena moves him away. "Katherine being gone, it doesn't change anything for you, does it?" he asks. "I wanna be with you, Stefan," she says, "You know that. But first, I need to wake up and know that the people that I love are safe. I need to feel safe. Do you understand?" Stefan says he does, even though he looks sad. Elena slowly walks away.

Katherine is seen waking up. She is in the tomb, but still has the moonstone. She wants to get out but she is trapped in the tomb by a new trapping spell. Damon appears outside of the tomb. When she asks him where she is, he says: "Where you should have been all along." She says he should have just killed her, but he retorts that death would have been too kind. Damon is almost done closing the heavy door to the tomb when Katherine pleads: "No. Damon, don't. Damon. Don't. You need me, Elena's in danger." Damon stops for a moment and furrows his brow. "From who?" he asks. Katherine refuses to answer. "You're lying," Damon says, "You're always lying." Damon closes the door further. "Why do you think I haven't killed her?" asks Katherine. "Because she's the doppelgänger! She needs to be protected." "Then I'll protect her," says Damon, "While you rot in hell." As he finally closes the door, Katherine starts screaming and begging desperately: "No. Damon, don't. I'll do anything, please, Damon, you need me. You need me. You need me!" She bangs her fist against the door and screams "You need me!" again, but Damon walks away, but not before swallowing hard.

Elena is in the driveway at the Lockwood's and is on the phone with Jeremy. "Yeah, Jeremy, I've got my car. I told Bonnie, whatever she did, I'm starting to feel better. Yeah, you can drive her home. I'm just gonna go straight to bed. OK." She hangs up and suddenly, a masked man appears behind her. Elena realizes someone's following her. She turns around and the man places his hand on her mouth so she can't scream and carries her away.