Meredith and Derek find that "happily ever after" isn't as easy as they hoped, Cristina finds interest in a military doctor, and the Chief is surprised to hear that Seattle Grace is no longer ranked as a top-tier teaching hospital.

As a group of best friends deal with the aftermath of their car crash, Dr. Torres takes the lead on a groundbreaking course of treatment for one of the patients. Meanwhile, Major Hunt starts to irritate other attendings with his presence in the hospital.

There is a huge problem affecting the whole hospital including patients too. Richard is trying to do his best to solve the problem.

Callie worries over her first real date with Erica. Cristina stumbles upon a neglected area of the hospital.

Bailey's dream of a domino surgery crumbles when one of the donors learns of her husband's affair. Meredith is insulted when she gets no credit for the procedure she and Derek worked on together.

The new trauma surgeon shocks everyone with his methods, Bailey is asked to save a girl with an inoperable tumor, and Callie's not sure what she wants.

The residents and interns squabbling over procedures upsets Dr. Hunt, Erica discovers what happened to the heart she lost, and Derek asks Sloan to break out the McSteamy to distract Yang.

Izzie wrestles with her ghost, Torres uses a ground-breaking procedure to get her mind off of Hahn, and the interns continue teaching themselves spurred on by a new cohort.

Sadie manipulates the interns into performing a procedure that goes horribly wrong, Izzie's ghost refuses to leave, and Mark bonds with a girl who's taken responsibility for her sleep-walking father.

The residents make their cases for the solo surgery, Sadie chafes at her restrictions, and Sloan battles his desires.

Derek has trouble with objectivity concerning his death row patient, Cristina and Meredith continue their feud, Izzie confides her problem to Alex, and the Chief faces what's become of his life's work.

Derek's mother visits, the death row patient starts angling for death in the hospital, Izzie craves more in her relationships, and Jackson's need for organs becomes critical.

Meredith and Miranda each cross a line, William Dunn regrets his decision and Izzie finally confronts what Denny's appearance means.

Cristina carries on an intense flirtation with Owen, Derek gets advice from everyone on how to propose, Izzie gets some tests done, and Bailey's promotion may stand in the way of a new career possibility.

Owen runs into someone very special from his past. Izzie employs her fellow doctors in a medical game made to help teach the interns. Naomi, Sam and Addison rush Archer to Seattle Grace and meet with Derek and Mark to save his life.

Addison and Derek differ on the treatment plan for their patient, Cristina discovers malpractice in high places, Izzie gets bad news, and Mark spectacularly mistimes his confession.

Derek's malpractice deposition reveals an unhappy statistic, the interns finally diagnose 'Patient X', Karev stands up to two attendings to save a band geek, and when Webber shuts Miranda out completely she makes a call.

Sloane's facial transplant fades to the background as the interns begin squabbling, Bailey's attempts to reach Derek unexpectedly clear surgeons from the hospital, and Cristina juggles her first solo surgery with treating a resistant Izzie.

Owen's PTSD endangers Cristina, Izzie's illness leaves the residents dealing with guilt and anger - at her expense, and Derek's fear causes him to persevere for Meredith's answer.

Izzie bites off more than she can chew on her first day of chemotherapy, Mark and Derek are forced to work on the same patient, Meredith's plans for a simple wedding take a turn, and Karev finds himself split between worry over Izzie and excelling as a resident.

Izzie's mother comes to town, a little girl shoots her father triggering a conflict between Meredith and the chief, Thatcher reappears, and Callie gets her first taste of life without her trust fund.

A car crash involving students going to their college graduation takes its toll on the residents in the ER, Derek's wedding gift is uniquely suited for Meredith - even if the oversight is not. Meanwhile, Denny's return has Derek and Bailey searching for the cause, and the results will change the outcome of the day.

Izzie is torn over whether to have Derek's proposed brain surgery. A soldier on medical leave asks for a radical operation so he can return to active duty. The Chief tries to lure Bailey back to general surgery with a new toy, and Mark shifts into high gear with major life changes.

Izzie's memory problems panic Alex, the team takes care of a John Doe who was hit by a bus, Bailey rethinks her pediatrics fellowship, and the hospital endures losses.