Dude. This episode was so great! I know I say that all the time for this, but come on! I was so sure this was gonna be an Elena/Katherine who is who at the masquerade ball. And it was so much better than that!
So, we've all got a part in the plan to kill Katherine. Jeremy, Caroline, Stefan, Damon, and Bonnie are all in on it. Elena is left out for her own saftey.
However, it turns out, Katherine has yet another ace up her sleeve. She's got a witch that binds herself to Elena so when Stefan and Damon try to kill her, Elena feels that pain. She's so fucking smart. I hate it. Of course, this immediately makes the brothers change course.
Lucy, pissed at being exposed, tells Bonnie that she should trust her (which she does because of outside forces- turns out they're related), does some kind of spell on the moonstone that causes Katherine to not be able to breathe. I have to tell you. I'm unsure about this play. Yes, it works for everyone, but if we're gonna incapacitate Katherine, shouldn't it be on of use? Not someone we just met this episode?
Anyway, they weakens Katherine enough that Damon can lock her in a tomb. She pleads for him to let her out. Tells him that she can help keep Elena safe. Especially since she is a doppelgänger and that's important for some reason. Honestly, I'd love if we got a better explanation of why Katherine and Elena look alike and why it's important to save Elena because of it.
Elsewhere, Matt is trying to carry out his promise to Katherine. However, Caroline here's the struggle and shows up, breaking the boys apart. When she successfully saves Tyler, the other girl (also under the thrall of Katherine), stabs him and he instinctively pushes her away. She ends up bashing her head on a table and dying. Meaning, Tyler is now a werewolf.
However, Caroline covers for him and tells him she has a pretty good idea of what he is. I'm not sure exactly what's going on here, as she knows that werewolves can kill her with one bite. But I think, maybe, she's genuinely just a good person, and is trying to help other other humans. You guys, Caroline is turning into one of the best characters. You did not steer me wrong!