Season 4:

- Meredith's long lost half-sister, Lexie, makes a splash on the scene as the new intern under Cristina. Meredith and Lexie aren't the best of friends at first, but eventually both come around and become close.

- Guess what? Meredith and Derek break up AGAIN. It's okay though, they both are coping by having sex with each other all the time. They like to label their little liaisons as S&M, or "sex and mockery."

- Meredith starts therapy. This wasn't the easiest road for her. She admits to her psychologist that she witnessed her mother attempt suicide (not really though, it was a cry for help). Thankfully therapy helps and Meredith works through a lot of her issues.

- Meredith and Derek's relationship gets a little complicated with the introduction of Nurse Rose. Derek likes Rose AND Meredith; Meredith dislikes Nurse Rose. Needless to say this situation is a little complicated. By the end, Nurse Rose is out and Meredith decides that she'll try to trust Derek. Mer-Derk is back! Cue passionate kiss