In the two hour fifth-season opener, Meredith and Derek discover the morning-after side of their renewed relationship; a military doctor (Kevin McKidd) who arrives at the hospital with a trauma patient catches Cristina's eye; and the chief learns that Seattle Grace's national rankings have slipped.

Second hour of the season five preimere, Meredith and Derek discover the morning-after side of their renewed relationship; a military doctor (Kevin McKidd) who arrives at the hospital with a trauma patient catches Cristina's eye; and the chief learns that Seattle Grace's national rankings have slipped.

A plumbing leak becomes a deluge and wreaks havoc at Seattle Grace, as the Chief attempts to implement new teaching policies and George tries to retake his residency exam. Meanwhile Derek hopes to make some changes at Meredith's house.

Meredith gets upset when Derek finds her mother's diary; Callie worries about her first "official" date with Erica; and Cristina discovers a part of the hospital that neither she nor her fellow residents had seen before.

Bailey heads up a "domino procedure," in which each surgery hinges on the one preceding it. Meanwhile, Derek gets sole credit for the brain-tumor study he did with Meredith; Lexie tries to get George to notice her romantically; and Sloan counsels a desperate Callie in the ways of love. Someone reappears and other peolple relationships evolve.

The chief gives Bailey new power and responsibility. He also gives her a very difficult surgical assignment: remove a girl's inoperable tumor. Meanwhile, new trauma chief Owen (Kevin McKidd) challenges the attendings' methods and the residents' skills.

The Chief tells the residents that one of them will get a solo surgery, and a competitive frenzy ensues; Derek asks Bailey for advice when he feels that Cristina is coming between him and Meredith; Erica discovers a shocking connection between one of her residents and a longtime patient.

Meredith's old friend Sadie (Melissa George) becomes an intern at Seattle Grace, but Meredith's other friends aren't exactly welcoming; new surgeon Virginia Dixon (Mary McDonnell) brings rules and order to the OR; and Lexie leads the interns in secretive, unorthodox surgical-training sessions.

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.

Cristina is awarded the first solo surgery among the residents, but she has to relinquish it and choose her replacement; Mark performs a cutting-edge procedure to restore a patient's speech, impressing Lexie in the process; and Callie can't figure out if Sadie (Melissa George) is flirting with her or just being friendly.

Bailey teams with Seattle Grace's new pediatric surgeon, Dr. Arizona Robbins, to save the life of a young patient near and dear to her heart, as the admittance of a passing row inmate at the hospital stirs anger in Derek and further erodes Meredith and Cristina's friendship; meanwhile, Callie and Sloan work as a team to fight their respective attractions to Sadie and Lexie, and Izzie tells Alex that she's seeing Denny.

Derek's mother, Carolyn, makes a surprise visit to Seattle and meets Meredith for the first time, as Mark tries to conceal his relationship with Lexie from her as well; meanwhile, passing row inmate William wishes to donate his organs to Bailey and Arizona's patient, as Owen and Cristina try to go on their first date.

Bailey grows desperate as a patient's condition becomes more and more dire. Everyone in the hospital is stepping up to try to find the boy a new organ donor, including Meredith, who considers a passing row patient's wish to die before execution. Meanwhile, an injury leaves Mark in a compromising position in the OR and Cristina awkwardly avoids Owen.

Now that Derek has the engagement ring, he searches for the perfect way to propose to Meredith, as Lexie demands that Mark go public with their relationship, and Bailey, encouraged by her work on recent cases and by Dr. Dixon, considers a new direction for her medical career.

Addison, Naomi and Sam rush the ailing Archer to Seattle Grace and reunite with old friends Derek and Mark to help save his life; meanwhile, Izzie employs her fellow doctors in a medical game designed to help teach the interns, and Owen runs into a significant someone from his past.

Derek's confidence is shaken like never before as he faces off with Addison over what course is best for their dying pregnant patient; Cristina calls the abilities of a renown surgeon into question after she botches a standard procedure; and Bailey, who has decided to pursue a fellowship in Pediatrics, is appalled by the Chief's less-than-stellar recommendation letter.

After learning at a deposition that more of his patients have died than survived, Derek decides to quit, even as Meredith refuses to give up on him. Meanwhile Bailey and the Chief continue to bicker over her peds fellowship until Adele steps in to mediate. The interns discover something unsettling on a "patient x," unaware that the charts they're looking at are actually Izzie's.

After his fellow surgeons try and fail to bring Derek back to work, Meredith must summon the strength to convince him. Meanwhile the hospital is abuzz as Mark attempts a rare face transplant surgery. Cristina, at last awarded her first solo surgery, is more focused on the needs of her friends, and Izzie does her best to keep her medical condition a secret.

All eyes are on Derek as he is set to perform his first surgery after his breakdown; attention is also set on Izzie, whose medical condition requires her to undergo a difficult surgery; and Owen has another PTSD episode that injures Cristina and traumatizes both of them, throwing the future of their relationship into question.

Izzie works on planning Meredith and Dereks wedding all while receiving intense treatment to battle her cancer. While George gets back in the game excelling at a trauma emergency, Alex freezes up. Owen seeks help for his PTSD from a familar face. Callie's father comes to visit and Callie introduces her new girlfriend Arizona much to his dismay.

As preparations continue for Meredith and Derek's wedding, several residents must face the arrival of their parents at the hospital: Izzie's mother Robbie causes a stir when she pays a surprise visit, and Thatcher returns to make amends with Meredith and Lexie. The Chief clashes with Meredith over a controversial medical case.

As Meredith, Derek and all of their friends prepare for the big wedding, a group of college students, injured in a car crash as they were heading to their graduation ceremony, is admitted to the ER. Meanwhile, Izzie fears the worst when she begins experiencing familiar symptoms.

In the first part of the two hour season finale, Izzie spends time with a fellow cancer patient and contemplates whether or not to undergo a risky surgery, as Mark is ready to take his relationship with Lexie to the next level and a patient makes Owen reassess his place at Seattle Grace.

In the second part of the two hour season finale, George delivers stunning news to Bailey, sending shockwaves throughout the hospital, and Izzie's friends anxiously await her recovery from surgery. Meanwhile Bailey is surprisingly displeased after being accepted into the pediatric fellowship program, and the victim of a near-fatal traffic accident brings the talents of Seattle Grace's doctors together.