The interns, now residents, deal with their own crops of interns. Callie struggles with her new position, and Burke makes a decision.

Lexie persists in trying to get to know Meredith, and Mama Burke descends once more.

Callie hides in her office, frustrating Bailey who's itching to teach someone. Elsewhere, age becomes the theme as Izzie tries to convince 'Really Old Guy' he shouldn't die, Webber and Sloan set out to prove they're not too old to learn a new technique, and Karev is saddled with an intern who's past his prime.

Meredith and her intern lose a patient after they give her the wrong diagnosis, Callie confronts Izzie, and McDreamy bonds with the other Grey.

Meredith feels she's being haunted by her Mother's ashes, and Cristina is denied a surgery for a surprising reason.

A man survives a parachute accident without serious injury, two women refuse treatment because of a wedding contest, and Cristina and Izzie jockey for inclusion in Hahn's surgeries.

Hahn bans Cristina from her service, Bailey covers more and more of Torres' duties, and Izzie and George go to extreme lengths to recapture the magic of their first encounter.

Bailey crosses the line when the guy she had a crush on in high school shows up in the ER during an onslaught of high school students involved in a bus crash. The Grey sisters run and hide when their father shows up drunk, while Derek tries to get back into the dating scene with another doctor and Cristina tries her best to get back into Hahn's good graces.

An accident in the ER bay leaves two paramedics fighting for their lives, and a third who refuses Bailey's care. Meanwhile, Alex juggles two women, and Lexie begins to bond with a patient.

Tragedy abounds for everyone at Seattle Grace as they all continue in efforts to get the paramedic out of the overturned ambulance, stop the bleeding of a man who won't quit, and a bigot with a Nazi tattoo on his stomach. On the personal side, Rebecca returns to spend time with Alex, Miranda's husband finds it harder to wait for her while she's in surgery, and Cristin...

Bailey's son comes to the ER, Derek takes a housing step that puts pressure on Meredith, Izzie has a crisis of faith, and Cristina's choice may change her course with Hahn.

The judgment of the residents is skewed by a competition, Meredith tries therapy and a bear attack may be more than it appears.

Addison is not prepared for all the changes that greet her upon her return to Seattle Grace for a specialized surgery, Meredith and Derek begin their clinical trial, Izzie feels left out, and Karev is confronted with an unexpected announcement.

The new clinical trial patient has a secret, Yang is dealt a blow from a distance by Burke, the nurses refuse to work with Sloan, and Meredith's therapist tells her some home truths.

Cristina is still in her slump and turning mean, Izzie finally confronts Ava/Rebecca, and Meredith's anger with her therapist is challenged by a patient with a Cinderella story.

A surgical team battles the clock as they try to save a boy encased in cement, Karev's situation with an ever-disintegrating Ava brings back painful memories that interfere with his judgment, Derek and Meredith have one last chance at their clinical trial.

Meredith and Derek are at odds over whether or not to continue with their 13th clinical trial patient and the doctors lift the final critical pieces of cement from the young boy's body. Meanwhile, Alex rushes Ava into the hospital and is forced to confront the reality of her condition.