The attendings vie to be Chief. Two people who haven't slept together before, will. McSteamy's 60-day vow of chastity has a conclusion. We meet a boss, his assistant, and his wife. We also get to see someone being treated in the clinic. Derek has more questions about his relationship with Meredith. The chairman of the hospital board is admitted as patient. Callie confronts Izzie about her relationship with George.

A patient comes to the ER with a dream and a condition which may prevent him form realizing it. Two patients are competing to win something big. One of them convinces an intern to take their place.

There has been a bus crash and the patients are in the ER. Meredith and Derek's relationship gets more complicated when he dates a fellow doctor. Meredith's dad goes to visit her at the hospital.

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.

As preparations continue for Meredith and Derek's wedding, Izzie receives a surprise hospital visit from her handful-of-a-mother, Robbie. Meanwhile, a newly sober Thatcher visits his daughters, Meredith and Lexie, in order to make amends, and the Chief and Meredith bitterly fight over a controversial medical case.

When Meredith and Lexie's father, Thatcher, returns to the hospital with a failed liver, it's up to Meredith to save his life. Meanwhile, Izzie empathizes with a patient riddled with tumors, as Mark, annoyed with Cristina's competitive zeal, tricks her into assisting on an unusual surgery.

Bailey preps the team with mandatory sensitivity training prior to admitting a 700-pound patient with compounded medical issues, and the case proves to be challenging in every sense of the word. Meanwhile Derek has to come face to face with a former patient's husband in a wrongful death deposition, and spending time with a heart patient's daughter opens up some old wounds for Cristina.

Meredith finally tells Derek about her pregnancy and miscarriage; during a surgery, Cristina experiences PTSD; Bailey won't let Alex operate until he has the bullet in his chest removed.

Personal and work pressures are adding up and have Meredith visibly on edge, Owen conducts formal interviews for the Chief Resident position, Cristina grows increasingly defiant, Alex and Lucy's undefined relationship gets tested, and Jackson suddenly backs out of the Webber's diabetes trial.

A stampede at a comic book convention leads to an influx of colorful characters in the ER; Mark continues to make life difficult for Jackson; Ben returns and realizes Bailey has moved on.