In the first, Caroline's father kept her prisoner and tried to train her to associate pain with blood. He said it was for her own good. But eventually Tyler and Caroline's mom came to her rescue, with this plot concluding with Caroline crying into Tyler's arms.
Then, there was the big stuff:
- We flashback to 1920s Chicago often because that's when Stefan was at his Ripper-est. We learn he and Klaus were actually good friends and Stefan was dating Klaus' sister, Rebecca. So, what happened? The police - with wooden bullets! - came to the club one night and Klaus left with Rebecca in a hurry because "he" was coming. He glamoured Stefan to forget about them and told Rebecca later on she had to choose between Klaus and Stefan.
She chose Stefan and Klaus killed her.
- But he woke her back up in real time because a witch in Chicago said she needed Rebecca's help to contact the original witch and figure out what happened with the hybrid transformation error. One problem, said Rebecca (who was also reunited with Stefan, who Klaus UNglamoured and who remembered the entire past): the answer lay with her necklace... which Stefan picked up back in the day and which Elena now wears.
- Stefan also came face to face with Elena in present time and told her to leave. Klaus cannot know she's alive and that is why his hybrid process didn't work.
- And finally we learned that Katherine is hanging out in Chicago these days.
Source: TV Fanatic