Jeremy and Bonnie chat about her magic as they wait for their signal from the Salvatores. Jeremy's feeling his oats. "Can you do a hocus-pocus and ace a test?" When Bonnie says she doesn't play that way, Jeremy replies, "That would be like the first one I'd learn... Or maybe like a sex spell, or something. I don't know." Bonnie's bedazzled masquerade mask can't hide the fact that Bonnie's eyes are bugging out of her head, but Jeremy's high on vampire hijinks and hormones, so he proposes they dance to pass the time until the Salvatores text them. At first, Bonnie laughs her ass off, because this is her BFF's little brother, y'all. Then she considers his...well, his clean-haired Jeremy-ness, and amends her answer to a polite, "No, thank you." Damon then sends a "Now" text to the Germ, saving him from any further awkward advances. Since he's up, Jeremy finds Katherine, and pretends he thinks she's Elena until Lucy leaves them. Once they're alone, he tells Madame KaKa to meet the Brothers Salvatore at the edge of the Lockwood Lake, down by the woods. After Katherine leaves him, Elena pops out of nowhere and pulls Jeremy aside. "What the hell is going on?"
Katherine hasn't un-lived this long by being stupid, so rather than running right to our beautiful brothers, she throttles Caroline in some remote corridor of the mansion. Oh, she pretends she wants intel from her baby-vamp, but we all know this is really all about the show's Obligatory Throttling of the Week (OTotW). After the OTotW, Caroline leads Katherine to the enchanted upper room, but it's only once Katherine has crossed the threshold, and Caroline has not, that KaKa learns Bonnie has sealed her sassafras in there. It's like the tomb, but more well-appointed.
Stefan and Damon do their damnedest to kill Katherine, but she really does have plans for every letter of the alphabet, so it's tougher than you'd think (or hope). They battle it out with their cheating ex until Jeremy rushes upstairs and informs the Brothers Salvatore that anything anyone does to Katherine also manifests on the ever-fair form of our Miss Gilbert. So far, they've staked KaKa in the back (missing her pre-Christmas Grinch-sized heart), and stabbed her in the arm. And our Elena? She's hurting because of it. Once Katherine has this confirmation, she inflicts some gratuitous self-harm, just to freak out our pretty boys. Outside, poor Elena suffers and bleeds.
Bonnie can't reverse the spell linking Elena to Katherine, but she can cast a spell to relieve Elena's pain, so she does, because duh, they're BFFs. When Jeremy returns, Bonnie leaves him with Elena and rushes off to find Katherine's witch. Upstairs, Katherine taunts Stefan with Damon's feelings for Elena, but Stefan is focused and doesn't let her get to him.