Cristina and Meredith's surgical skills are put to the ultimate test.

Seattle Grace Hospital is hit with a crisis like no other in its' history.

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. This is the second hour of a 2-hour season finale.

It's all hands on deck at Grey Sloan when a group of medical students is injured by a floor collapsing at their white coat party. Jo and Link are forced to talk about the future, while Jules confronts Winston about his attitude.

Meredith is brutally attacked by a patient, and Penny is the one who discovers her. The doctors of Grey Sloan Memorial rush to stabilize Meredith and remain by her side in the harrowing aftermath.

Dr. Arizona Robbins returns to Grey Sloan for a particularly complicated case. The interns are interrogated about their past mistakes, while Teddy is eager to return to work after her health scare.

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.

Derek is still operating when he finds out about Meredith's current situation. Meredith is freaking out about her situation. Webber and Bailey are dealing with medical health issues. Cristina and Izzie have their own issues to deal with because of Meredith's situation. Addison freaks out when George tries to find a solution to Bailey's impromtu postponement. Overall, Seattle Grace Hospital is still under code black and the situation is getting worse.

Meredith is still underwater, but nobody seems to notice. Her worsening condition makes her rescuing an urgent matter. Derek finds her coat on a man she had helped, and starts looking for her and, much to his shock, the little girl Meredith took care of suggests that she is in the water. Derek saves her, but she is almost dead, due to hypothermia. Izzie has to perform brain surgery on a man stuck between cars, as he begins to experience seizures. She drills holes into his head, perforates his skull and ultimately saves his life before he is rescued and transferred to Seattle Grace Hospital. George lies to the woman whose son he had been looking for, in order to get to surgery, but still doesn't have any luck in locating him. Alex finds no hope in searching for the pregnant Jane Doe's family as she undergoes surgery. The interns find out about Meredith's situation and express their hopelessness. She wakes up in what appears to be limbo and meets her deceased acquaintances.

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 death 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.

After a burn victim unexpectedly dies in the midst of a chaotic ER, the Chief and board member Jennings interrogate the residents to find the culprit, as all the Mercy West and Seattle Grace resident defends their actions in an effort to save their jobs.

When a trauma patient arrives at Grey Sloan, it forces Jo to confront her past. Meanwhile, Bailey and Ben have to talk to Tuck about dating.

Train Wreck victims come to Seattle Grace and all staff gets called in. Everyone deals with really weird cases. Except Addison and Izzie. They work with a woman who is pregnant.

An explosive case arrives at the O.R. that might endanger all the lives of the people working there, which leads Dr. Burke to declare a "Code Black" for the hospital. Bailey worries where her husband is as she is in labor. Also Izzie and Alex may be creating some heat.

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.

Grey Sloan Memorial Hospital enters crisis mode as the storm rages, resources become scarce and patients flood in by the busload. Meanwhile, one of the doctors fights for their life.

In this Amelia-centric episode, Amelia engages in the surgery of a lifetime as a crowd of doctors look on from the gallery. With Stephanie by her side, she begins operating on Dr. Herman, but quickly realizes it's far more difficult than she anticipated. Meanwhile, Bailey becomes skeptical when Arizona takes on one of Herman’s cases.

In the midst of the sisters’ dinner party, Maggie ditches her cooking duties to rush to the hospital. Meanwhile, April steps in to help cook as an attempt to avoid Jackson, and Arizona nervously waits to find out more about Callie’s new girlfriend.

A mass trauma situation, which turns out to be a ferryboat accident, challenges the whole staff of Seattle Grace Hospital. Richard finds difficulty in coping with his separation from his wife and dyes his hair "for the ladies", which becomes an internal joke between Mark, Burke and Derek. Cristina tries to tell Meredith about her upcoming marriage, but doesn't have the strength to. George promises to find a woman's son, who has been separated from her at the accident. The woman refuses to go into surgery until she is assured that her son is alive. Izzie has to take care of a man who got stuck between two cars on the ferry, but nobody helps her due to the large number of injured people. Alex rescues a pregnant woman with severe wounds on her face, and promises to take care of her. Meredith looks after a girl who has been separated from her mother after the accident, but accidentally falls into the water and drowns, with nobody but the little girl as a witness.

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.

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.

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 his new role as Chief, Derek restores the hospital lecture series, and Richard, Bailey and Callie present to the group pivotal surgical cases from their pasts Bailey reflects on her first days as a shy resident, Callie looks back on a polio case, and Richard recalls a case in which he and Ellis worked on a patient diagnosed with GRID, a virus later called AIDS.

In this flashback episode, return to the site of the plane crash and watch as each doctor tries to cope with the heartache and injuries caused by the crash. Meanwhile, back at Seattle Grace, everyone struggles to find a bit of normalcy amidst the chaos.

Meredith and Amelia work to secure funds for their research while Amelia finds herself at odds with a new attending. Levi runs into someone from his past, and Owen gives Winston advice. Lucas ditches Mika, forcing her to treat a patient alone.