How does a person who prides herself on being in total control lose it? Why is there an out of control party in my living room?
The answer to all of these questions could only be: Derek.
After George and Nora's marriage, the Mc Donald's moved in with the Venturis in London, Ontario.
Casey was originally upset about having to move to London, Ontario from Toronto, a much bigger city (as shown in the episode "How I Met Your Stepbrother"), for many reasons including Derek, but she eventually got over her own problems and agreed to move there for Nora and George's sake once she saw how much they cared for each other.
She thinks she and George should be the happy, dancing people. They calm down as Tuck is in the room and Bailey reminds him he volunteered to stay home and take care of the baby. She's talking about not caring about Lexie and Thatcher, but Derek comments she talks about them an awful lot for someone who doesn't care. Sloan has gathered a lot of doctors and nurses in Nick Hanscom's room. Mark is impressed by his own success, but there's only a delicate flap of skin between his carotid artery and the outside world. If that happens, Mark says it's their job to stop the bleeding and then page him. The paramedics get ready to leave as there's a pile-up on the freeway, so they're busy.