The fifth season concludes with George making a stunning announcement, Bailey questioning her pediatric fellowship program, and Izzie’s fate hanging in the balance.

The first of a two-part season finale finds Izzie fighting for her life as Mark and Owen contemplate their future relationships and careers.

As Grey’s Anatomy turns 100, Meredith and Derek prepare to walk down the aisle as Izzie’s condition brings back familiar (handsome!) symptoms.

As preparations continue for Meredith and Derek’s wedding, her father returns to make amends. Izzie receives a visit from one of her estranged parents, as well.

Izzie plays wedding planner to take her mind off her treatment, while Callie introduces Arizona to her disapproving father, and Owen seeks help for his PTSD.

Derek returns to the OR after his meltdown, while Izzie’s condition requires her to undergo an operation of her own.

Cristina and Izzie debate what do to next, while Mer attempts to get Derek out of the woods and back to work.

Derek decides to quit, but Meredith refuses to give up on him. Bailey and the Chief continue to bicker, while Izzie’s interns discover something unsettling.

Derek may not be a god after all. But he can sure throw a mean right cross.

Derek and Addison square off yet again – this time with a patient’s life in the balance. Bailey, meanwhile, is stunned by Richard’s recommendation letter.