Season 4
* 01. A Change Is Gonna Come 27/09/2007
Meredith and Cristina return from Cristina's honeymoon to find that Burke is long gone. Izzie, Alex, Meredith and Cristina start their first day as residents, each with their own set of interns. Among the interns are George, who is repeating his internship after failing the exam, and Lexie, Meredith's half-sister. Meanwhile, Derek begins to look elsewhere after his relationship with Meredith hits an emotional impasse; Bailey grapples with the fact that her former interns now report to Callie, the new Chief Resident; and Richard returns to his position as Chief of Surgery.
* 02. Love/Addiction 04/10/2007
The interns and residents treat victims of an apartment complex explosion as Alex looks into the cause of the devastating accident. Mama Burke arrives at Seattle Grace to pick up the rest of Burke's personal things while Cristina trades wedding gifts for surgeries. Meanwhile, Lexie tries to talk to Meredith, who is less than willing to do so; Callie deals with the stress of being Chief Resident; and Bailey tries to figure out what to do with her excess leadership skills.
* 03. Let the Truth Sting 11/10/2007
The new interns are in awe of fellow intern George's skill level, and Lexie tries to keep his "repeater" status secret. Meredith comes to Lexie's aide when Lexie is faced with her first emergency situation. The Chief and Sloan have to use a radical surgery to save a woman's vocal ability. Meanwhile, George debates telling Callie about his affair with Izzie.
* 04. The Heart Of The Matter 18/10/2007
Izzie reveals her true feelings for George to one of her and George's friends, and the reaction she receives is not what she expected. Meanwhile, Adele Webber rushes her niece to Seattle Grace; Derek gives Cristina pointers on how to be a better teaching resident; and Norman, the world's oldest intern, misdiagnoses Meredith's patient.
* 05. Haunt You Every Day 25/10/2007
It's Halloween at Seattle Grace and the day is chock-full of surprises for the doctors. Alex has a surprise visit from a former patient; Meredith thinks her mother's ashes are haunting her; Cristina is snubbed by a top surgeon; and everyone is shocked when Callie reveals George and Izzie's relationship to the public.
* 06. Kung Fu Fighting 01/11/2007
With his marraige once again falling apart, Chief Webber invites the male surgeons out on a "gentleman's evening." Meanwhile, Cristina and Izzie compete for the same surgeries, mainly to impress the doctor performing them; Meredith treats the survivor of a skydiving accident; and two finalists competing in a promotional competition are treated by the doctors.
* 07. Physical Attraction... Chemical Reaction 08/11/2007
George and Izzie's relationship is tested, as is Derek and Meredith's when Derek wants more than a physical relationship with her. Meanwhile, Mark falls for a surgeon and Callie's position as Chief Resident is put on the line when she gives too many duties to Bailey.
* 08. Forever Young 15/11/2007
The ER is thrown into a state of chaos following a school bus accident. Meanwhile, Bailey treats her high school crush; Derek goes on a date; and Thatcher comes to Seattle Grace in search of Meredith.
* 09. Crash Into Me (Part 1) 22/11/2007
Meredith and the Chief rush to the scene of a devastating ambulance crash in which the lives of the paramedics are at stake. Bailey treats a difficult patient and Ava returns to find Alex with a new girlfriend.
* 10. Crash Into Me (Part 2) 06/12/2007
In the conclusion to the two-part episode arc, Meredith races to save the life of a paramedic, who is trapped inside an ambulance. Meanwhile, the life of a patient is in Lexie's hands and Derek and a nurse work together to save the life of a patient.
* 11. Lay Your Hands On Me 10/01/2008
Bailey's family faces a medical trauma, just as her marriage is falling apart, a surprise visit from George's mother comes as a shock to both Izzie and Callie, a faith healer challenges Erica and Alex's beliefs in traditional medicine, and Derek must deal with the aftermath of his kiss with Rose.
* 12. Where The Wild Things Are 24/04/2008
Six weeks following Derek and Meredith's break-up, Derek continues to date Rose while Meredith, Alex, Izzie and Cristina compete in a surgical contest. Meanwhile, George and Lexie adjust to their new apartment and Callie finds a new friend in Erica Hahn.
* 13. Piece of My Heart 01/05/2008
Addison makes her return to Seattle Grace in order to perform an operation. As she does so, she is preoccupied by all of the changes in her former co-workers' lives. Meanwhile, Meredith and Derek's clinical trial has its first patient, and Rebecca returns to deliver Alex some shocking news.
* 14. The Becoming 08/05/2008
The nurses' outcry over McSteamy's frequent trysts leads the hospital to enact a new "date and tell" policy. Meanwhile, news about Burke's career force Cristina to cope with her feelings about the past; Meredith and Derek take in a veteran soldier to participate in their clinical trial; and Callie finds comfort in Sloane when she needs it the most.
* 15. Losing My Mind 15/05/2008
As Dr. Wyatt refuses to let Meredith give up on her therapy sessons, Alex learns the truth about Rebecca's condition. Chief Webber has Dr. Hahn perform a high-risk surgery on his mentor. Meanwhile, after hearing about Burke, Cristina continues to act unusually, going as far as to clean her ever-messy apartment.
* 16. Freedom 1 & 2 22/05/2008
In the two-part season finale, Meredith and Derek take another shot at the clinical trial while the others race to free a boy from a hardening block of cement. Meanwhile, Izzie helps Alex care for Rebecca and Lexie learns a secret about George's intern status.
* 17. Freedom (2)
In the two-part season finale, Meredith and Derek take another shot at the clinical trial while the others race to free a boy from a hardening block of cement. Meanwhile, Izzie helps Alex care for Rebecca and Lexie learns a secret about George's intern status.
