In part two of the two-hour season finale, Cristina and Meredith’s surgical skills are put to the ultimate test, and the game changes for all the characters.

In part one of the two-hour season finale, Seattle Grace Hospital is hit with a crisis like no other in its history. Guest star Mandy Moore plays Mary, a patient of Bailey’s.

In “Shiny Happy People”, an elderly patient admitted into the E.R. for a heart condition sees a familiar face. Karev treats a troubled teenage patient, Hayley (guest star Demi Lovato). Meredith tells Cristina her suspicions regarding Owen. Read our full recap below!

In “How Insensitive”, Bailey preps the team with mandatory sensitivity training. Derek comes face to face with a former patient’s husband in a wrongful death deposition. Old wounds are opened for Yang. Read our full recap to see what happened!

Sloane returns to Mark’s apartment, just as she’s going into labor. Meanwhile Teddy sees Derek’s invitation to illustrious cardiothoracic surgeon Tom Evans’ as a threat to her future employment at the hospital, and the team work on a crab boat captain who has been stabbed with a giant shark hook. Read our full recap to find out what happened!

In “Sympathy for the Parents”, Alex’s younger brother, Aaron, shows up at Seattle Grace-Mercy West with a hernia, it’s up to Alex to get Bailey’s approval for his pro bono surgery. Matters are further complicated when Aaron discloses that his family has not heard from Alex since he arrived in Seattle, and parts of Alex’s past long kept secret are revealed to his friends and fellow doctors. Read our full recap to find out what happened!

In “Suicide is Painless”, Teddy’s patient seeks to end treatment and her life, turning to Hunt for help. The situation triggers Hunt’s memories of his life at war and his past relationship with Teddy.

A patient needs an extremely difficult surgery and Richard and Owen vie for it, leaving Derek in a difficult bind yet again. Bailey nervously prepares for another date with Ben.

Dr. Harper Avery is rushed to Seattle Grace-Mercy West, and the staff is surprised to discover that one of their own is related to this medical legend, whose requests flummox Derek and Richard.

A flashback episode sheds light on the affair between the Chief and Ellis in 1982. Separate 2004 sequences show Bailey in pre-“Nazi” days and Callie before she was introduced.