Meredith having a huge breakthrough with her personal life including Derek and her mother. Derek also realized he continually failed Meredith. Meredith and Derek preformed clinical trials on patients with brain tumors. They lost all of their patients except for one whose boyfriend died just before her life saving surgery.
After finally succeeding, Meredith finally took a risk and reunited with Derek. Almost all the cast had a kiss, including Meredith and Derek, George and Lexie, Richard and Adelle, Alex and Izzie, and, Erica and Callie.
We also learned about Alex's needy mother and part of his past. After Meredith and Derek's resumption of their relationship, Derek left to break up with Rose, his girlfriend who had come between the two previously.