The mountain climbers lie about the axe in their friend's head, telling Derek that it accidentally got there. During surgery, he and George discover that it was deliberately put there, and one of the climbers admit that he was trying to "put him out of his misery". Adele is saved after Richard finds her lying in the bathroom and is stabilized, but soon suffers a miscarriage. Richard learns Adele was actually pregnant with his son, not someone she had one night stand with. Bailey is disappointed to see that Callie is the new Chief Resident and begins to question her abilities as a surgeon. Richard chooses Derek as Chief of Surgery, but he refuses, telling him that he isn't done doing what he does best. Cristina and Burke's wedding day arrives, but Cristina won't stay out of the hospital. However, Cristina's nervousness results in Burke's realizing that he does not love the real Cristina and leaves her. Meredith and Derek are uncertain about their future and despite Derek admitting that she is the love of his life, they call their relationship over.

It's Halloween at Seattle Grace! There may be jokes, pranks, and/or scare tactics. Some of the women form a club based on an experience they all share. A man volunteers for what most of the doctors believe is an unnecessary surgery. One of the patients is in the hospital because they tried to carve a pumpkin in an unconventional manner.

An ambulance crash endangers the lives of the paramedics involved, as Meredith and the Chief work on-site to save them, Bailey treats a patient who refuses her help, and Ava returns for Alex and meets his other girlfriend in the process.

Meredith works furiously to save a paramedic trapped in an ambulance; Lexie holds the life of a patient in her hands; Derek must rely on a nurse to save a patient; Bailey struggles to balance her personal life with her work.

Dr. Wyatt refuses to let Meredith give up on therapy. Alex learns something else about Rebecca. The Chief wants Erica to perform a daring surgery. Christina continues to act strangely.

A couple undergoes surgery. Derek and Meredith's clinical trial gets a second shot from a new patient. Izzie helps Alex. McSteamy hooks up with someone.

A couple undergoes surgery. Derek and Meredith's clinical trial gets a second shot from a new patient. Izzie helps Alex. McSteamy hooks up with someone.