Cristina is awarded the first solo surgery among the residents, but she has to relinquish it and choose her replacement; Mark performs a cutting-edge procedure to restore a patient's speech, impressing Lexie in the process; and Callie can't figure out if Sadie (Melissa George) is flirting with her or just being friendly.
Meredith, Cristina and Bailey come to Lexie and Sadie's rescue when a routine surgery goes horribly wrong, as Owen and Derek treat a man seriously injured while sleepwalking and Mark comforts the sleepwalker's distraught daughter.
Meredith's old friend Sadie (Melissa George) becomes an intern at Seattle Grace, but Meredith's other friends aren't exactly welcoming; new surgeon Virginia Dixon (Mary McDonnell) brings rules and order to the OR; and Lexie leads the interns in secretive, unorthodox surgical-training sessions.
The Chief tells the residents that one of them will get a solo surgery, and a competitive frenzy ensues; Derek asks Bailey for advice when he feels that Cristina is coming between him and Meredith; Erica discovers a shocking connection between one of her residents and a longtime patient.
The chief gives Bailey new power and responsibility. He also gives her a very difficult surgical assignment: remove a girl's inoperable tumor. Meanwhile, new trauma chief Owen (Kevin McKidd) challenges the attendings' methods and the residents' skills.
Bailey heads up a "domino procedure," in which each surgery hinges on the one preceding it. Meanwhile, Derek gets sole credit for the brain-tumor study he did with Meredith; Lexie tries to get George to notice her romantically; and Sloan counsels a desperate Callie in the ways of love.
Meredith gets upset when Derek finds her mother\'s diary; Callie worries about her first \"official\" date with Erica; and Cristina discovers a part of the hospital that neither she nor her fellow residents had seen before.
A plumbing leak becomes a deluge and wreaks havoc at Seattle Grace, as the Chief attempts to implement new teaching policies and George tries to retake his residency exam. Meanwhile Derek hopes to make some changes at Meredith\'s house.
Part two of the two-hour season premiere. The Chief watches in amazement as the hospital\'s number of patients is increasing. Rose accidentally stabs Derek with a scalpel and Alex is offended when Izzie talks about him to Meredith. All the while, a deadly ice storm rages in Seattle.
A new Doctor comes to the hospital and starts to work there.