Elena creeps Stefan out by staring at him in bed. They make out. She has to leave to decorate the Lockwood house. He's going too so he can keep an eye on Mason. They worry that Katherine will find out they've been fake fighting. He sucks a little of her blood and they exchange vows of love. Meanwhile, Katherine rolls around in bed with Mason. She nibbles on him and they talk about the moonstone and exchange vows of love.
Jeremy tries barging into Damon's to tell him all about the Lockwood's. Damon's interest is piqued about the moonstone. Alaric shows up and they go over the research they have about curses and how the moonstone might be a way to break it.
The Lockwood mansion is being prepared for the masked ball. Bonnie and Elena argue about how they never see each other. Elena pulls her away to the woods and tells her about her problems. Bonnie wonders where they stand. They head back, where Mason is shocked to see Stefan is still alive. He walks away, bumping into Bonnie. She has a vision of Mason kissing Elena and tells Stefan. He realizes it must have been Katherine she saw. Inside, Damon tells Elena that her brother is working with him. She's not happy. He's snippy and plods off. The Salvatore brothers meet outside to discuss Mason and Katherine. They watch as Jeremy approaches Tyler about the stone and is told that Mason has it now. The brothers grab Bonnie. Damon asks her not to play morality police and just help them. She goes off and finds Mason, casting a spell to knock him out. The brothers chuck him in an SUV and drive off. They take him to their place and tie him up. She feels the werewolf's head and says the stone is in a well. She runs off and Damon slaps Mason awake. He heats up a poker and begins torturing him for information, though he's not happy that he heals quickly. Jeremy drifts in with some wolfsbane so Damon tests Mason to see how toxic it is. When he threatens to take his eyes out, Mason tells him that he wanted the stone to stop the curse and be with Katherine. "She's using you you moron," Damon says. After he kicks Jeremy out, he tears Mason's heart from his chest.
Caroline goes down to the underground crypt to see her mom. Liz refuses to speak to her, just like before she was a vampire. "Are you really dead?" she asks. "Yes and no," her daughter says. She tells her all about how she controls her cravings. Caroline goes upstairs and awkwardly chats with Bonnie. They go off in search of the well. Back at the Lockwood's, Matt worries Caroline is seeing someone. Stefan walks out and Elena trails after him. They go down to the well. When he hops down, his skin starts peeling off and he screams for help because it's filled with verbane. Caroline speeds over followed by Bonnie. They lower Elena down to pull Stefan up. As she finds the stone, she's attacked by an eel so Caroline pulls her up. Elena sits by Stefan and feeds him her blood. Caroline returns to the crypt to tell her mom about her day. Her mom's amazed by how strong she's become and agrees to keep her secret. Although they've never been so close, Caroline hypnotizes her to forget all of this so she can return to normal.
Back at the Salvatore's, as Stefan makes faces, Damon takes Mason's phone and calls Katherine to taunt her about her dead boy toy. She says she has plenty of alternative plans. She immediately calls Elena to taunt her about everything she knows and how she convinced Jenna to kill herself. When Elena turns around, Jenna stabs herself in the gut. They take her to the hospital, where she is saved. Elena weeps about what happened to her aunt and he promises that Katherine will pay. She goes to see Stefan and tells him they've been stupid to sneak around. "It's over," she says. They weep and kiss goodbye. As she runs out, Damon stops her and apologizes. "Katherine won," she says. Meanwhile, Tyler goes home where he is told by his mom that Mason went back to Florida. Across town, Katherine recruits Matt to incite Tyler to kill him and bring on the curse.
Cryptic commentary: They sure seem to spend a lot of time decorating for parties. Wow, what a gory and angsty episode. I feel kind of bad that they killed Mason, but it really showed how cold blooded Katherine is. The scenes with Caroline and her mom were really good and sad. It was nice to see more of Bonnie. Elena and Stefan breaking up again was kind of lame though.