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Derek s wife, Addison, a surgical superstar from New York, is in Seattle to perform a fetal-heart operation. Derek isn t pleased to see her, and Meredith is feeling very betrayed.

While Meredith and Cristina lick their wounds, they re kept busy in the extremely overbooked OR. Two of the cases stem from a car wreck caused by an alcoholic wife beater whose biggest advocate is his wife. Then there s a man with an obstructed bowel.

Addison (Kate Walsh) has divorce papers prepared; now all that she and Derek have to do is sign them. Meanwhile, Cristina, recovering from emergency surgery, proves to be an impossible patient, particularly when her mother is at her bedside.

Lightning knocks out the power to the hospital, which leaves Alex and George stuck in an elevator with a patient---a police officer with a gunshot wound.

As Derek and Addison see a therapist to try to put their marriage back together, Meredith and the other interns “steal” a psych patient who says he s pregnant. He isn t, but he isn t crazy, either.

A young woman who was friendly with the Shepherds in New York arrives in Seattle and asks Addison to remove her uterus because she s at risk for cancer. But her husband objects because he wants children.

Owen recruits a fellow Iraq-war vet (Kim Raver) as the new cardiothoracic surgeon, and Cristina questions the move for both personal and professional reasons. Meanwhile, Izzie returns with her high-school mentor, who s seeking treatment for dementia.

The impending birth of quintuplets (and the surgeries on the newborns that are certain to follow) preoccupy the surgeons, but not completely: Burke gives Cristina a key to his apartment, but she s not overjoyed about it.

It s Christmas, but nobody s feeling the spirit, except for Addison and Izzie---and Izzie s mad at Addison. A very pregnant Bailey needs a rest but has a very busy day instead, and George must cope with an ulcer patient s annoying family.

The docs toast the New Year with a mandatory work limit, which Cristina finds constricting, and she complains about it to Bailey as they fly to harvest a heart for a patient with a crush on Izzie.

As the docs muddle through a nurses strike, Meredith makes a mistake treating an elderly patient, and it s caught by the patient s friends (June Lockhart, Betty Garrett and Rae Allen). Meanwhile, Izzie treats a pregnant teenager.

Christina Ricci guest stars in an episode in which a patient s arrival threatens the lives of everyone in the OR. There are also developments with Alex and Izzie. Dylan Young: Kyle Chandler.

Derek and Addison are shaken by the arrival of someone from their past; Burke learns Cristina s secret; and Meredith delves into her family s dirty laundry after a visit with her mother. Dr. Mark Sloan: Eric Dane.

Meredith and George have a work dispute; new mom Bailey treats Addison for a gynecological problem; and Alex grows jealous as Izzie showers attention on heart patient Denny Duquette (Jeffrey Dean Morgan).