I'm glad that Callie, Mark and Arizona seem to work out this whole situation. They are obviously happy but unfortunately Lexie isn't. I can't blame her. Every time she decides to be with Mark he is doing something that hurts her. Is it possible for them to be together? I'm not sure anymore but I hope so.
Derek made a mistake not inviting Meredith to help with the Alzheimer's clinical trial. She has a lot of experience because of her mother and she is certainly a better person for it than Alex. Karev's decision to leave was definitely a good choice. It might be hard for Derek to work with Meredith though.
Cristina is back in the game! Poor Jackson didn't know what had hit him. I love their rivalry.
Dr. Lucy Fields had a hard time with Callie but luckily she is immune to panic-struck women and quite patient.
I didn't find the Twitter plot very exciting but Chief's comment to Owen about Bailey "tweets" was priceless:)
All in all another good episode of GA:)