Derek and Addison's relationship is rocked to the core when a former friend comes to Seattle Grace and his presence promises to shake things up for a few members of the staff. Burke and Cristina's relationship is affected when one of her secrets is outted. Alex and Izzie are having similar reactions to their closet scenes during the Code Black crisis. On top of this a cocky doctor shows up to piss Derek off in all kinds of ways. A patient is suffering from constant orgasms and her condition sparks interesting conversations among the staff. George is trying to figure out how to get Meredith to see him as more than just a housemate. Another patient, that Derek is treating, is dealing with a rare disorder and needs his parents support and understanding. Burke has a patient who inspires him to talk to Meredith and Cristina about doing what they say they will. Meanwhile, Meredith learns more about her family (in fact maybe more than she may have wanted to know) through her parents.

Denny needs a heart or else. Izzie and George go crazy trying to get him one. Derek has the life of a friend in his hands as he operates on Burke who has been shot. Burke cannot operate on Denny after Denny's heart stopped and now Denny is in a dire condition. Cristina gets put in charge of the ER and she is worried about Burke.

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.

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.

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.

Entering their first year as residents, Meredith Grey, Cristina Yang, Izzie Stevens and Alex Karev now have interns of their own to mentor. Among the new interns are George, forced to repeat his internship after failing his exams, and Lexie Grey, Meredith's half-sister. Another two new interns will be introduced in this season premiere. And they'll have their hands full when a three-car accident sends multiple casualties pouring into Seattle Grace. Some of the doctors need to deal with new stressed out interns. A young boy brings his bleeding deer to the hospital in the hope a doctor will save her.

There has been a bus crash and the patients are in the ER. Meredith and Derek's relationship gets more complicated when he dates a fellow doctor. Meredith's dad goes to visit her at the hospital.

Time has passed but not much has changed. Sexual angst still runs rampant in the halls of Seattle Grace. Derek and Rose have been dating and Meredith has noticed the activities of her current off-again ex-boyfriend. The doctor's are in the midst of a competition.

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.

As Meredith and Derek begin to find that their "happily ever after" is anything but easy, Cristina develops a crush on a military doctor who brings in a trauma patient. Meanwhile, the Chief and his staff cope with the news that Seattle Grace is no longer considered a top-tier teaching hospital.

Alex is offended when Izzie talks about how great a man Alex is to Meredith. Derek is stabbed with the scalpel in the palm of his hand by Rose, while the Chief is stunned over Mercy West's increase in the number of patients, a deadly ice storm ravages Seattle.

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 death 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 decides to quit after learning that more of his patients have died than survived; Izzie's interns make an unsettling discovery about "Patient X."

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

Owen recruits Dr. Teddy Altman, a former Iraqi veteran, as the new cardiothoracic surgeon. Cristina questions her abilities in the E.R. and relationship with Owen. Izzie returns to Seattle Grace with her high school mentor seeking treatment for his dementia. Richard's responsibilities, post-merger, are taking a toll on him.

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.

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

In the wake of the shooting at Seattle Grace-Mercy West, the doctors find themselves in a frenzy: Christina and Owen will be getting married, and others are trying to deal with the recent blood bath. Derek is arrested for speeding!

Meredith, looking to prove she is Chief Resident material, learns that anything and everything can happen in an hour's time when she steps up to run the ER for a night; meanwhile, Bailey sneaks off with Eli and gets into a little mischief, and everyone is surprised when the Chief's wife, Adele, shows up as one of the ER patients.

News of Meredith's dishonesty in the clinical trial comes to light, leading to unanticipated consequences for her and others; Cristina finds herself in a compromising situation, which forces her to decide between her career and her relationship; Owen posts his decision for Chief Resident, and Teddy makes a surprising choice regarding her love life -- and her future.

The fifth-year residents return for the first day of a year that will make or break their careers: Meredith faces the consequences of tampering with Derek's clinical trial and is terminated at the hospital; April tries to step up to the plate as Chief Resident in the wake of a giant sinkhole in the middle of Seattle; and Cristina and Owen are still at odds over their drastically different feelings for their unborn child.

News of Meredith and Derek's unsteady relationship raises a red flag for Zola's adoption counselor; Alex quickly realizes that he has become the outcast of the group after ratting out Meredith; and Cristina makes a tough decision regarding her unexpected pregnancy. Also, Chief Webber brings Henry in for a last minute surgery, alarming Teddy.

This is an historic episode that finally crosses a long-standing barrier.

In the spirit of Valentine's Day, Meredith and Derek try to have a night to themselves when Lexie offers to watch Zola; Callie hands babysitting duties over to Mark so that she can surprise Arizona with a romantic evening; and Ben proves to Bailey that he knows her better than she thinks. Meanwhile, the ER fills with romantics, including a 10-year-old girl who has an allergic reaction to chocolates from her valentine and a man who is hit by a car while chasing down his frustrated girlfriend.

Faced with a life threatening situation, the doctors must fight to stay alive while trying to save the lives of their peers; Bailey and Ben make a decision regarding their relationship; and Teddy is presented with a tempting offer. Meanwhile, Richard plans a special dinner for the residents.

The doctors of Seattle Grace are faced with the aftermath of last season's plane crash. As they try to move on with their lives, they must learn to adapt to the changes, cope with their losses and move forward with their relationships and careers.

As the rest of the doctors prepare for Bailey's wedding, Richard helps her through a bout of pre-wedding jitters. Meanwhile, Lizzie butts heads with Meredith, and Callie and Jackson try to convince Derek to participate in a risky surgery that could fix his hand.

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.

The Grey Sloan Memorial Hospital doctors are faced with the devastation left by the storm. A giant mudslide in Seattle injures a group of first responders and citizens, causing the already short handed ER to spring into action. Meanwhile, Meredith is faced with a tough decision that will affect the life of a loved one, Callie is rocked by the reality of Arizona’s infidelity, and Richard’s life is in extreme danger.

The doctors of Grey Sloan Memorial throw a fundraising gala which turns wildly competitive after Jackson makes a rash promise. Back at the hospital, Bailey’s patience is tested when she has to deal with several extremely difficult patients. Meanwhile, Shane and Stephanie handle an incredibly busy ER by themselves and Alex reveals an emotional secret to Jo.

The doctors are faced with the consequences of the events at April's wedding. Alex reacts to the news about his father. Callie and Arizona make a decision about their relationship.

Cristina considers her future at the hospital; Amelia and Derek collaborate on a tough surgery involving conjoined twins; Jo takes on too many cases at once; Stephanie stumbles on the truth about Bailey's case.

Maggie tries to make a good impression but finds herself in unfortunate situations; Richard keeps hiding his secret.

Owen tries to get Callie to help Veterans Hospital patients with the robotic limb lab. Alex and Meredith's friendship makes Jo jealous. Alex and Bailey prepare to go in front of the board.

Maggie and Meredith disagree with Derek about the best way to approach a patient’s case, which leads to a bigger argument between the couple. Meanwhile Callie feels responsible when one of her veterans is pushed too far and one doctor’s routine procedure results in a devastating diagnosis.

As the doctors continue to tackle an unfathomable crisis, they are reminded of what is important and are brought closer together.

Maggie reevaluates her life choices after receiving an invitation to her ex-boyfriend’s wedding; Richard questions Bailey’s loyalty, and Jo confides in Stephanie about a secret she’s been keeping from Alex. Meanwhile, Alex struggles with making a difficult decision that will affect the lives of newborn twins.

Midseason Finale - As the rumor mill around the hospital continues to spiral out of control, Grey Sloan Memorial is flooded with injured firefighters from a nearby wildfire. Maggie struggles to keep things with Andrew professional at work; meanwhile, Jo questions Alex’s priorities.

The evolution of April and Jackson’s relationship is revealed through a series of flashbacks dating back to when they first met. Simultaneously, we follow the years-long progress of one of Jackson’s patients.

Owen and Amelia take their relationship to the next level; Alex gains some clarity on his future with Jo; and Callie and Arizona continue to struggle with the current custody arrangement.

A car crash at a funeral brings a bickering family into the hospital. Back from New York, Arizona ends up caught between Alex and Andrew. While Ben takes on a new parenting role, Amelia helps Meredith and Maggie through a problem.

Believing he is going to jail tomorrow, Alex makes a big decision about his future. While the hospital is overrun with victims of a building collapse, Richard demands answers from Bailey about Eliza’s presence at Grey Sloan.