So, Elijah wakes up eventually, and it seems like he's in pain. He also, repeatedly calls Elena, Katherine. Once Elena assures him, he's Elena, he starts to writhe in pain. Turns out, he hasn't been invited into the house and he need to GTFO. Elena helps him to the front door. The two of them set up a wary truce, and Elena gives him the dagger to prove he can trust her.
Stefan calls her while she's with Elijah and is not happy, but Elena convinces him to let her do this her way. And if Stefan is unhappy, Damon is livid.
But we get some back story, turns out Elijah and Klaus are brothers. And, the sun and moon curse is fake. However, Klaus is a vampire/werewolf hybrid and some witches put a curse on him to suppress his werewolf half so he wasn't too powerful. Breaking the curse actually means that Klaus can become both vampire and werewolf. The way to break it is the same, but the outcome is different. Elijah also tells Elena what we already know, that we need a super powerful witch to break the curse.
However, we also find out that Elijah had found a way to protect the doppelgänger during the ritual so she wouldn't have to be sacrificed. (And he told Klaus this way back when, be he didn't care enough about human life to be interested). Oh yeah, and Elijah (like everyone else on this show) was in love with Katherine.
While all this is going on, Klaus (as Alaric) ends up telling Jenna about vampires. It's a very odd way to have this discussion, but I guess it gets the point across. Eventually, Jenna tells Klaus she wants him out. He refuses, so she goes to leave, but he pulls a knife on her. Stefan grabs the knife and pins Alaric to the wall screaming at Jenna (with his vampire face) to leave. He then calls Elena and tells her what's up. She tries to talk to Jenna about, but she's still freaked out. Obviously. Especially, when she finds out basically everyone knows about vampires except her.
Elena and Elijah go back to the original deal where everyone she loves will be safe from him. And all he asks in return from Damon and Stefan is an apology. Stefan obliges, Damon, not so much. So, Stefan and Damon are fighting because they are in love with the same girl. Nothing new here.
And finally, Klaus gets a witch and some other chanty people to get him out of Alaric's body and back into his own. Where has this body been?
Oh, and Damon brought Katherine some vervain. Although, I'm not really sure why.