Derek and Addison are shaken by the arrival of a figure from their past. Meanwhile, Burke learns Cristina's secret, Izzie deals with a very unusual case, Meredith delves into her family's dirty laundry, and George pours his heart out.

Izzie copes with her grief by baking furiously, and George has to deal with an obstinate patient. Meanwhile, Meredith must choose between Derek and Finn, Addison drowns her sorrows in alcohol, and Cristina meets Burke's difficult mother.

Izzie returns to the hospital, but finds it difficult to go inside, and George is tired of Callie's presence at home. Meanwhile, Addison cannot seem to get rid of Mark, and Cristina tries to cope with caring for Burke.

Meredith becomes a patient, and Derek and Addison are equally angry at Richard for allowing Mark to join the staff. Meanwhile, Izzie receives a visit from Denny's father, and Burke is plagued by doubt over his ability to return to surgery.

Guilt causes different actions in everyone, the interns are allowed to attend an M&M meeting, and Derek and Addison finalize things.

Izzie returns to the hospital under probation, and George tries to make amends with Callie. Meanwhile, Cristina's deletion of Bailey's name on Burke's OR board makes her assume he is against her, and Derek's irritating sister Nancy visits.

Derek, George, Alex, Burke, Richard, Joe and Walter go on a camping trip. Meanwhile, Meredith assists Mark with gender reassignment surgery, Izzie avoids discussing her grief, Addison works with Callie, and Cristina feels Bailey's wrath.

George must deal with his family's presence when his father is admitted. Meanwhile, Burke's secret is almost out, Alex tries to get close to Izzie again, and Richard comes to a decision about his marriage.

A traumatic car accident fills the ER. Cristina has a crisis of conscience about her deceptive teamwork with Burke, Izzie pushes the boundaries of her probation, and Callie tries to explain herself to George.

Bailey is adamant that Burke and Cristina should be punished, Derek doubts his abilities, Izzie tries to take a stand against Mark's patronizing behavior, and Meredith deals with family in two very different ways.

As George's father's surgery approaches, he begins to realize how serious his condition is. Meanwhile, Izzie has to prove to Bailey that she is ready to scrub in on a surgery, and Meredith keeps running into her father.

George's father's surgery has left him very weak, Izzie's act of generosity backfires on her, Cristina and Burke continue their war of silence, and Meredith reaches out to her father.

George deals with his grief, Cristina and Burke continue to ignore each other, Addison avoids Alex, and Izzie decides to help Bailey with a project. Meanwhile, Richard makes a decision which sends all the attendings scrambling.

A toxic patient wreaks havoc. Meanwhile, Bailey opens the free clinic, but the lack of patients makes Izzie question her investment. Meredith's mother is admitted again, and Cristina makes Burke wait for an answer.

The interns each react differently to a mass-casualty incident. Meanwhile, George crosses the professional line with Callie, Cristina asks Burke to keep quiet about their engagement, and Richard dons a new hairstyle.

Izzie fights to save her patient's life, George searches for the son of his patient, and Alex has to contend with the relatives of victims. Meanwhile, Meredith is unconscious underwater, with Derek her only hope.

An unconscious Meredith interacts with some ghosts from her past while Richard, Burke and Bailey devise an unusual method of reviving her. A despondent Cristina leaves during her shift, and Derek speaks his mind to Meredith's mother.

A Korean war veteran with a bullet lodged in his shoulder is admitted. Meanwhile, tensions escalate between Izzie and George, Callie reveals a big secret, Cristina contends with an old flame, and Alex continues to work with the Jane Doe.

The attendings face their board interviews. Meanwhile, Izzie seems to be the only one who remembers the night before, Derek is overly protective of Meredith when Mark offers her a surgery, and Callie's father pays a visit.

Meredith deals with her over protective stepmother, Cristina is caught between Burke and Marlow, and Derek fights to become Chief. Meanwhile, Alex continues the search for Jane Doe's identity, and Izzie's past comes back to haunt her.

The Chairman of Seattle Grace's board of directors is admitted, and the attendings vie for his favor, while the interns study for exams. Izzy and George are reminded of their infidelity, and Burke presses Cristina about wedding plans.

Addison heads for warmer climate to figure things out, Meredith's stepmother visits the clinic, Cristina's perfect wedding is challenged when she and Burke's mothers visit, and Izzie tries to talk to George.

Addison is pulled into the case of a high-risk surrogate mother, Meredith's stepmother develops a complication, Izzie struggles with George's decision, and Ava has surgery which may restore her memory.

The interns face their first year medical exams. With the interns busy, the attendings must do their own legwork, Burke appoints a new best man, Cristina writes her vows, and Callie grows suspicious of George and Izzie.

The wedding day arrives. Richard chooses the new Chief and Chief Resident, the interns receive their exam results, Callie drops a bombshell on George while Izzie pours her heart out to him, and Burke makes an important decision.

The interns, now residents, deal with their own crops of interns. Callie struggles with her new position, and Burke makes a decision.

Lexie persists in trying to get to know Meredith, and Mama Burke descends once more.

Callie hides in her office, frustrating Bailey who's itching to teach someone. Elsewhere, age becomes the theme as Izzie tries to convince 'Really Old Guy' he shouldn't die, Webber and Sloan set out to prove they're not too old to learn a new technique, and Karev is saddled with an intern who's past his prime.

Meredith and her intern lose a patient after they give her the wrong diagnosis, Callie confronts Izzie, and McDreamy bonds with the other Grey.

Meredith feels she's being haunted by her Mother's ashes, and Cristina is denied a surgery for a surprising reason.

A man survives a parachute accident without serious injury, two women refuse treatment because of a wedding contest, and Cristina and Izzie jockey for inclusion in Hahn's surgeries.

Hahn bans Cristina from her service, Bailey covers more and more of Torres' duties, and Izzie and George go to extreme lengths to recapture the magic of their first encounter.

Bailey crosses the line when the guy she had a crush on in high school shows up in the ER during an onslaught of high school students involved in a bus crash. The Grey sisters run and hide when their father shows up drunk, while Derek tries to get back into the dating scene with another doctor and Cristina tries her best to get back into Hahn's good graces.

An accident in the ER bay leaves two paramedics fighting for their lives, and a third who refuses Bailey's care. Meanwhile, Alex juggles two women, and Lexie begins to bond with a patient.

Tragedy abounds for everyone at Seattle Grace as they all continue in efforts to get the paramedic out of the overturned ambulance, stop the bleeding of a man who won't quit, and a bigot with a Nazi tattoo on his stomach. On the personal side, Rebecca returns to spend time with Alex, Miranda's husband finds it harder to wait for her while she's in surgery, and Cristina still tries to get on Hahn's good side, even though Bailey has put her elsewhere.

Bailey's son comes to the ER, Derek takes a housing step that puts pressure on Meredith, Izzie has a crisis of faith, and Cristina's choice may change her course with Hahn.

The judgment of the residents is skewed by a competition, Meredith tries therapy and a bear attack may be more than it appears.

Addison is not prepared for all the changes that greet her upon her return to Seattle Grace for a specialized surgery, Meredith and Derek begin their clinical trial, Izzie feels left out, and Karev is confronted with an unexpected announcement.

The new clinical trial patient has a secret, Yang is dealt a blow from a distance by Burke, the nurses refuse to work with Sloan, and Meredith's therapist tells her some home truths.

Cristina is still in her slump and turning mean, Izzie finally confronts Ava/Rebecca, and Meredith's anger with her therapist is challenged by a patient with a Cinderella story.

A surgical team battles the clock as they try to save a boy encased in cement, Karev's situation with an ever-disintegrating Ava brings back painful memories that interfere with his judgment, Derek and Meredith have one last chance at their clinical trial.

Meredith and Derek are at odds over whether or not to continue with their 13th clinical trial patient and the doctors lift the final critical pieces of cement from the young boy's body. Meanwhile, Alex rushes Ava into the hospital and is forced to confront the reality of her condition.

Meredith and Derek find that "happily ever after" isn't as easy as they hoped, Cristina finds interest in a military doctor, and the Chief is surprised to hear that Seattle Grace is no longer ranked as a top-tier teaching hospital.

As a group of best friends deal with the aftermath of their car crash, Dr. Torres takes the lead on a groundbreaking course of treatment for one of the patients. Meanwhile, Major Hunt starts to irritate other attendings with his presence in the hospital.

There is a huge problem affecting the whole hospital including patients too. Richard is trying to do his best to solve the problem.

Callie worries over her first real date with Erica. Cristina stumbles upon a neglected area of the hospital.

Bailey's dream of a domino surgery crumbles when one of the donors learns of her husband's affair. Meredith is insulted when she gets no credit for the procedure she and Derek worked on together.

The new trauma surgeon shocks everyone with his methods, Bailey is asked to save a girl with an inoperable tumor, and Callie's not sure what she wants.

The residents and interns squabbling over procedures upsets Dr. Hunt, Erica discovers what happened to the heart she lost, and Derek asks Sloan to break out the McSteamy to distract Yang.

Izzie wrestles with her ghost, Torres uses a ground-breaking procedure to get her mind off of Hahn, and the interns continue teaching themselves spurred on by a new cohort.

Sadie manipulates the interns into performing a procedure that goes horribly wrong, Izzie's ghost refuses to leave, and Mark bonds with a girl who's taken responsibility for her sleep-walking father.

The residents make their cases for the solo surgery, Sadie chafes at her restrictions, and Sloan battles his desires.

Derek has trouble with objectivity concerning his death row patient, Cristina and Meredith continue their feud, Izzie confides her problem to Alex, and the Chief faces what's become of his life's work.

Derek's mother visits, the death row patient starts angling for death in the hospital, Izzie craves more in her relationships, and Jackson's need for organs becomes critical.

Meredith and Miranda each cross a line, William Dunn regrets his decision and Izzie finally confronts what Denny's appearance means.

Cristina carries on an intense flirtation with Owen, Derek gets advice from everyone on how to propose, Izzie gets some tests done, and Bailey's promotion may stand in the way of a new career possibility.

Owen runs into someone very special from his past. Izzie employs her fellow doctors in a medical game made to help teach the interns. Naomi, Sam and Addison rush Archer to Seattle Grace and meet with Derek and Mark to save his life.

Addison and Derek differ on the treatment plan for their patient, Cristina discovers malpractice in high places, Izzie gets bad news, and Mark spectacularly mistimes his confession.

Derek's malpractice deposition reveals an unhappy statistic, the interns finally diagnose 'Patient X', Karev stands up to two attendings to save a band geek, and when Webber shuts Miranda out completely she makes a call.

Sloane's facial transplant fades to the background as the interns begin squabbling, Bailey's attempts to reach Derek unexpectedly clear surgeons from the hospital, and Cristina juggles her first solo surgery with treating a resistant Izzie.

Owen's PTSD endangers Cristina, Izzie's illness leaves the residents dealing with guilt and anger - at her expense, and Derek's fear causes him to persevere for Meredith's answer.

Izzie bites off more than she can chew on her first day of chemotherapy, Mark and Derek are forced to work on the same patient, Meredith's plans for a simple wedding take a turn, and Karev finds himself split between worry over Izzie and excelling as a resident.

Izzie's mother comes to town, a little girl shoots her father triggering a conflict between Meredith and the chief, Thatcher reappears, and Callie gets her first taste of life without her trust fund.

A car crash involving students going to their college graduation takes its toll on the residents in the ER, Derek's wedding gift is uniquely suited for Meredith - even if the oversight is not. Meanwhile, Denny's return has Derek and Bailey searching for the cause, and the results will change the outcome of the day.

Izzie is torn over whether to have Derek's proposed brain surgery. A soldier on medical leave asks for a radical operation so he can return to active duty. The Chief tries to lure Bailey back to general surgery with a new toy, and Mark shifts into high gear with major life changes.

Izzie's memory problems panic Alex, the team takes care of a John Doe who was hit by a bus, Bailey rethinks her pediatrics fellowship, and the hospital endures losses.

Covering days one through 13, everyone at Seattle Grace fights to save Izzie and George's lives and then deals with the aftermath. Elsewhere, Hunt treats a double amputation, and Arizona has a teen with painful growth spurts.

During days 20 through 40 the staff continues toward acceptance. Meanwhile, Arizona takes a manipulative step to diagnose her pain patient and Hunt's amputee patient sinks into a deep depression.

As hospital personnel jockey for notice to keep from being fired, Izzie returns to surgery early and Bailey's triple aneurysm patient refuses her procedure because of her schizophrenic son.

Thatcher is hospitalized with liver failure, and Meredith fights anger and guilt while deciding her responsibility. Sloan treats an octogenarian who wants an implant. Izzie's interference in Hunt's cancer case may have deadly consequences.

As Mercy West merges with Seattle Grace, battle lines are drawn between the two hospital's residents over the patients.

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 residents defend their actions in an effort to save their jobs.

When Isaac, the hospital lab tech, has an inoperable tumor wrapped around his spine, he turns to Dr. Derek Shepherd to do the impossible, and Derek tests the Chief's authority when Richard objects to moving forward with the risky surgery.

A generous donation is offered to Seattle Grace by the parents of Arizona's 10-year-old patient. When his condition worsens, however, she finds herself with a conflict of interest. Meanwhile, Cristina tests her boundaries with Owen at the hospital and, adding insult to injury, Alex is left with all of Izzie's hospital bills to contend with.

When Owen recruits his fellow Iraqi War vet, Dr. Teddy Altman, as the new cardiothoracic surgeon, Cristina questions Teddy's abilities in the OR and the nature of their past relationship. Meanwhile Izzie returns to Seattle Grace with her high school mentor seeking treatment for his dementia, and the stress of Richard's responsibilities, post-merger, are taking their toll.

As Thanksgiving, Christmas and New Year's pass, Miranda is visited by her father, William, who disapproves of her choices in life; meanwhile, Mark and Lexie must cope with the shocking arrival of a woman from his past, and Thatcher Grey questions the Chief's recent behavior as Meredith comes to his defense.

Mark flies Addison to Seattle to help with a difficult procedure on his pregnant daughter, Sloan. Owen questions Teddy's motives when she assigns Cristina the lead on a complicated surgery, and Derek's suspicions are raised when the Chief recruits Meredith to assist with a high profile operation.

After learning of Richard's drinking problem, Derek confronts him for the sake of his friend and the hospital, Izzie returns, hoping to reconcile with Alex, and tensions run high between Teddy, Cristina and Owen in the aftermath of Cristina's startling confession.

An intra-operative crisis casts a shadow over Derek's first day as interim chief, Owen's influence worries Cristina, Karev's first pediatric surgery case turns out to be more than babysitting and Webber resents the decision he must make.

It's Valentine's Day and the doctors must treat dozens of injured people after the roof collapses at a popular romantic restaurant; Derek tries to manage his busy schedule as Chief of Surgery; Meredith wrestles with her new duties as the Chief's wife; and Mark and Callie team up to convince Sloane to do the right thing for her baby.

In his new role as Chief, Derek restores the hospital lecture series, and several attendings present to the group pivotal surgical cases from their pasts: Bailey reflects on how shy she was as an intern until getting advice from Webber, Callie looks back on a polio case, and Richard recalls a case in which he and Ellis worked on a patient diagnosed with AIDS, known in 1982 as GRID.

When Avery's grandfather comes to the ER, Webber's wish for a stress-free first day back is lost after the surgeon requests an awake surgery. Elsewhere, Cristina and Teddy attempt a hand-me-down lung transplant for a cancer survivor.

A patient who needs an extremely difficult surgery comes to Seattle Grace, and it's Richard and Owen who vie for the opportunity to tackle it. But the decision lies in the hands of Derek, who deems that Owen should take on the surgery, leaving Richard bitter. Meanwhile, Bailey deals with her own personal struggles when she nervously prepares for another date with Ben.

When Teddy's patient seeks to end treatment and her life, she turns to Hunt for help. The situation triggers Hunt's memories of his life at war and his past relationship with Teddy. Meanwhile, Callie and Arizona have a difference in opinion on what their future holds, and Richard tries to adjust to his role as a surgeon.

Alex' brother Aaron comes to Seattle with a hernia and needs a pro bono operation. Having children is on everyone's minds and tensions are high because of it.

Sloan returns to Mark's apartment just as she's going into labor. Teddy, Mark and the still-fighting Callie and Arizona are there to help with the birth and to get Mark through his grandson's pending adoption. Meanwhile Teddy sees Derek's invitation to illustrious cardiothoracic surgeon Tom Evans' as a threat to her future employment at the hospital, and the team work on a crab boat captain who has been stabbed with a giant shark hook.

Bailey preps the team with mandatory sensitivity training prior to admitting a 700-pound patient with compounded medical issues, and the case proves to be challenging. Meanwhile Derek has to come face to face with a former patient's husband in a wrongful death deposition, and spending time with a heart patient's daughter opens up some old wounds for Cristina.

An elderly patient admitted into the E.R. for a heart condition sees a familiar face, a long lost love who happens to be in the E.R. as well for a fractured arm, and the staff find themselves caught up in their love story. Meanwhile, Karev treats a troubled teenage patient whose parents brought her in for schizophrenia, and Meredith can't help but tell Cristina about her suspicions of Owen -- which inevitably messes with Cristina's head.

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

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

Dereks near death experience results in reckless behaviour; Meredith has trouble getting cleared for surgery in the wake of the shooting and Cristina & Owen take their relationship to the next level.

After weeks of concealing the fact she was pregnant and miscarried, Meredith at last tells Derek and is finally cleared to return to her surgical duties in the wake of the hospital shooting spree; Cristina experiences post-traumatic stress disorder in the midst of an operation; and Bailey refuses to let Alex operate until he agrees to have the bullet in his chest removed.

When Derek receives an unexpected and unwelcome visit from his estranged sister, Amelia, issues between the siblings -- both past and present -- come to the surface; the Chief tries to help Alex when he notices that he's refusing to use the elevators after his near-fatal shooting; and Meredith and Derek continue their efforts to ease Cristina back into surgery after her post-traumatic stress.

Things are hostile on all fronts when a visit to the obstetrician results in some disturbing news for Meredith and Derek and Lexie loses it when she notices Meredith and April getting closer. Meanwhile, a car crash brings in multiple traumas and Jackson tries using his physical attributes to get ahead in the operating room, while Cristina's self-doubt carries outside of the hospital and into her house-hunting with Owen.

As part of their training, the Chief puts Seattle Grace's residents -- including Meredith, Cristina, April and Jackson -- in charge; meanwhile, Derek, Callie, Owen and the other attending surgeons compete for a million-dollar grant.

A documentary film crew visits the hospital six months after the shooting to document the road to recovery for doctors and patients. The camera lenses follow Derek, Owen, Mark & Callie as they ambitiously perform a rare arm transplant surgery, Meredith helps Cristina put on a brave face for the cameras, and Bailey's patient, Mary, returns for her surgery -- which marks the first time they've all seen of each other since that fateful day.

The residents are pushed to their limits when Owen puts them through a rigorous trauma certification drill; meanwhile, Cristina is also tested when left alone to monitor a very ill lung transplant patient.

Top security measures go into place as a team of doctors, led by the Chief, try to save the life of a major political figure from the Middle East. Meanwhile Cristina decides to finally decorate her new place and throw a housewarming party, and Alex shows up late from a weekend getaway to his first day of rounds with the new Pediatrics Attending, Dr. Robert Stark.

Derek lands the grant he needs for his clinical trial and all the attendings take him out to Joe's Bar to celebrate, but they get a surprise when they see someone they know already at the bar. Meanwhile, Meredith and Alex have to fend for themselves during the night shift with a nine-year-old patient who's experiencing post-surgical complications and his very pushy mother.

Despite Meredith's objections to the idea, a concerned Derek takes Cristina on a fishing trip in order to get away from it all, while Teddy, feeling directionless without Cristina, directs all of her efforts and compassion towards a dying patient who lacks the proper insurance to seek medical treatment.

News of the incoming mass causalities after a gunman opens fire at a local college hits the staff hard when they must spring into action, even while their own wounds are still fresh; and Arizona does not receive a warm welcome home at the hospital.

Arizona seeks Mark's advice as she tries to reconcile with Callie, who has big news of her own; Teddy must make a key decision for Henry during his surgery; and on the same day the residents receive a new crop of interns, the Chief announces he is looking for a new Chief Resident.

Meredith feels left out when Derek breaks ground on his clinical trial; Bailey's new idea does not go over well with the chief; Callie irritates her new obstetrician.

Le père de Lexie revient à l'hopital avec des douleurs abdominales et une jeune fiancée. Alex se prend la tête avec la nouvelle obstétricienne. Mark fait du chantage à Jackson pour en apprendre sur Lexie.

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.

Meredith must choose between her fertility treatments and her eyesight when she begins having trouble seeing, Mark makes it clear to Callie and Arizona that he takes his role as father-to-be very seriously, and April discovers there's more to Dr. Stark than first appears.

Richard is desperate for Derek and Meredith to accept Adele into their Alzheimer's trial, but will Adele stand in her own way? Meanwhile Mark and Arizona have conflicting ideas of the kind of baby shower Callie wants, Teddy is freaked out when Henry has another health complication -- leaving them both a little exposed -- and the competitiveness amongst the residents for the Chief Resident position is amplified when Richard receives the green light for his diabetes clinical trial.

In a series first, the music that has been at the heart of the show and been beloved by fans comes to life for Grey's Anatomy: The Music Event. A cataclysmic event rattles the doctors of Seattle Grace to the core, as Callie, on the verge of an enormous life-changing moment with Arizona, envisions her hospital and friends as it has never-been-seen before. "Chasing Cars" (Snow Patrol), "How to Save a Life" (The Fray) and "The Story" (Brandi Carlile) are among the songs performed by the cast.

Everyone pulls together to help Callie and baby Sofia on their painstaking journeys to recovery in hopes of allowing mother and baby to finally meet; the sudden death of a clinical trial patient has Derek proceeding with more caution while Meredith makes a calculated and risky move; Alex treats a cranky old rich woman dying of cancer and gets an idea for a grandiose endeavor that is sure to get him the Chief Resident spot; and Teddy is pleasantly surprised by the return of a familiar face.

As Callie and Arizona's wedding approaches, the couple quickly realize that the day they've been looking forward to is not turning out the way they'd envisioned. Meanwhile Alex continues to make the other residents jealous as he appears to be the top contender for Chief Resident, Meredith and Derek make a decision that will change their lives forever, and Dr. Perkins presents Teddy with a very tempting proposition.

As the official Chief Resident interviews begin, everyone steps up their game in the hopes of impressing Owen. Meanwhile, Meredith anxiously prepares for her first interview with the social worker and Cristina fights for a shot in the operating room.

While Meredith faces the consequences of tampering with the trial Cristina and Owen fight over an unexpected pregnancy.

Meredith faces the repercussions of messing with the medical trial.

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.

The chief makes a decision that shocks everyone at Seattle Grace.

A stampede at a comic book convention leads to an influx of patients.

The residents try to impress Jackson's mother, Catherine Avery.

Lexie tries to get Derek interested in a patient's rare brain tumor.

Owen organizes a baseball game against Seattle Presbyterian.

Jackson's suspicions about Mark and Lexie interfere with work.

Teddy is called away on another case, as Henry is brought in for surgery.

Teddy asks Cristina to help with an OR patient.

The doctors form two teams to operate on conjoined twins.

While Derek prepares to operate on a tumor deemed entirely inoperable, Hunt pressures Meredith to declare a specialty. As Cristina and Teddy try to steal a prized cardio surgery, the doctors celebrate Richard's 10,000th surgery.

Meredith dreams of what her life would have been.

On Valentine's Day Lexie volunteers to watch Zola for Meredith and Derek; Callie plans an evening for Arizona; and Ben shows Bailey how much he cares. Meanwhile, Christina and Owen drift farther apart despite the fact that he saves her when a car crashes into the hospital. Meredith and Bailey treat a woman who has headaches and seizures. Webber and Lexie treat a man who was hit by a car during a fight with his girlfriend. Alex treats a 10-year-old girl who has a severe reaction to peanuts when her boyfriend gives her a Valentine's Day gift.

In a final attempt to save Erica's life, Amelia arrives at Seattle Grace to beg Derek for help with the gliosarcoma case; Cristina and Owen engage in heated arguments during marriage counseling; Alex realizes that in order to be a good doctor, he'll need to improve his people skills; and Meredith is given a chance to shine when a man enters the ER after getting his hand stuck in meat grinder. Meanwhile, the residents continue to study for their upcoming oral boards.

As Adele's condition continues to deteriorate, Richard considers altering their living situation; an explosion at a local coffee shop results in a busy day in the ER for the doctors; Callie takes Meredith under her wing by helping her study for her boards; Lexie joins Arizona and Alex in peds, as they continue to care for intern Morgan's premature son; and when Jackson snaps at a patient, Mark encourages him to find ways to relieve his stress. Meanwhile, Cristina lets her suspicions get the best of her.

Derek encourages a hesitant Meredith to work with him again in neurology. When she complies, she listens as Derek is talking to a patient, who excitedly tells him about how she passed out in the middle of a big job interview. They're going to remove a cyst that's causing seizures. There is also a benign tumor that they aren't going to remove. Just as the procedure is past the opening skull stage, Derek is called to another OR where Morgan's baby is suffering from a brain bleed. He tells Lexi and Meredith to carry on. A slight bleed leads to another chunk of skull being removed. This opens up sight of the benign tumor. They decide to remove it because access is already present. Derek is incensed when he returns. It wasn't in the plan. When the patient awakes, she is unable to speak. Her parents threaten to sue. Jackson's mother, Catherine Avery, returns to Seattle Grace with a urology fellow, to replace a faulty bladder with one that Richard and Miranda have grown in the lab. During the procedure, Catherine develops an interest in Richard, becoming quite flirtatious. The fellow, Dr. Mara Keaton, was brought to be a spy for Catherine about how her son is doing. Jackson is forced to take her on a hospital tour. He is instantly suspicious of her motives and calls her on it. She admits that she is supposed to gather information on him. In turn, he advises Mara on how she can assert herself and gain his mother's respect. They try it out, defying her intent to take them to an awards banquet. The two of them trip off to find an empty on call room to get to know each other better. Richard is asked to the award banquet but turns her down at the last minute. Cristina becomes increasingly suspicious of Owen's every move. She finally corners nurse Emily, her prime suspect, and asks her point blank about sleeping with Owen. Emily says no. She uses a bit of flirting to get through long shifts. When Christina faces Owen, he admits he has been unfaithful to her. Alex has been working continuously to save Morgan's preemie. Callie watches Alex and Morgan work together and sees that Morgan is falling for him. He denies it. But when Morgan has her picture taken with him and the baby, you can see it in her body language.

A pet lion on the loose gives the hospital some fierce injuries to deal with. Meanwhile, Cristina continues to ignore Owen, Lexie reconsiders her feelings for Mark, Callie has to face Arizona's romantic past with other hospital staff, and Alex starts to feel uncomfortable about his relationship with Morgan.

Grey, Bailey, and Webber work on a multi-organ transplant but run into some barriers when Dr. Sloan, the temporary Chief, orders them to cancel the surgery. Meanwhile, Cristina and Owen spend the day at home, working through their marital problems.

While the hospital becomes the center of attention as the victim of a famous kidnapping case is brought to the hospital, the fifth years take their placement interviews. Meanwhile, Adele Webber's memory continues to deteriorate, forcing Richard to reconsider their relationship.

As the fifth-years head off to San Francisco to take the most important exam of their lives there are some surprises along the way; Owen and Teddy continue to fight back at the hospital; Mark and Lexie reconnect; and Tommy's condition worsens.

Six hours after their oral boards, the fifth years relive their answers and worry about their chances. Back at the hospital, Bailey has to woo potential candidates for the hospital and Mark is startled when Julia makes a proposal about their future.

Before the Seattle Grace doctors head to Boise to take part in an operation on conjoined twins, the Attendings pressure the 5th years for final decisions on their posts next year. Meanwhile, Arizona must face the reality of her friend's condition and Ben tries to get Bailey to go on a special lunch date.

As Meredith, Cristina, Derek, Mark, Lexie, and Arizona face the aftermath of their accident, the doctors back at the hospital face the future that seems to be taking them all in different directions.

Months after the plane crash, the doctors at Seattle continue to try and find a new sense of normalcy. With a new set of interns to put through the ringer, the new fellows and attendings get used to their roles while Cristina adjusts to her new life in Minnesota. But the life of one doctor hangs in the balance and it's clear that Seattle Grace Mercy West is not the same.

Each of the doctors involved in the crash experiences flashbacks that take them back to their time of rescue and explain how they got to where they are now.

The survivors of the crash are presented with a settlement offer, which forces them to choose between putting the incident behind them or investigate the true cause. Meanwhile various events occur: Jackson and April struggle to work with each other, Bailey is annoyed by the new attendings' behaviors, Callie struggles to communicate with Arizona and Cristina learns to work with her new colleagues in Minnesota.

A small plane crash results in multiple casualties, bringing back terrible memories.

Meredith and Nathan must face their feelings when they end up next to each other on a plane.

The stress of managing the hospital and coming to terms with Ben's decision to become a Seattle firefighter pushes Bailey to her limits.

Meredith has a patient whose family is celebrating Day of the Dead, making the doctors remember loved ones they have lost. Richard shares unexpected news with Meredith about her father, Thatcher. Meanwhile, Teddy tries to tell Owen that she is pregnant but they get sidetracked, and Jo encourages Link to pursue one of the doctors.

Both a mother and daughter are in critical condition and fighting over the last ventilator. Meanwhile, Hayes' sister-in-law ends up in the hospital with a kidney stone, and the house has a few more kids join in as Amelia's the babysitter.

Jackson shares his big news with his colleagues while Koracick and Levi fight to save a pregnant woman's grandfather as she goes into labor. Maggie keeps a watchful eye on Meredith as Bailey and Richard put off telling her about DeLuca.

Months after the plane crash, the doctors at Seattle continue to try and find a new sense of normalcy. With a new set of interns to put through the ringer, the new fellows and attendings get used to their roles while Cristina adjusts to her new life in Minnesota. But the life of one doctor hangs in the balance and it's clear that Seattle Grace Mercy West is not the same.

Each of the doctors involved in the crash experiences flashbacks that take them back to their time of rescue and explain how they got to where they are now.

Sloan returns to Mark's apartment just as she's going into labor. Teddy, Mark and the still-fighting Callie and Arizona are there to help with the birth and to get Mark through his grandson's pending adoption. Meanwhile Teddy sees Derek's invitation to illustrious cardiothoracic surgeon Tom Evans' as a threat to her future employment at the hospital, and the team work on a crab boat captain who has been stabbed with a giant shark hook.

Derek's mother visits, the death row patient starts angling for death in the hospital, Izzie craves more in her relationships, and Jackson's need for organs becomes critical.

Izzie wrestles with her ghost, Torres uses a ground-breaking procedure to get her mind off of Hahn, and the interns continue teaching themselves spurred on by a new cohort.

Derek and Addison are shaken by the arrival of a figure from their past. Meanwhile, Burke learns Cristina's secret, Izzie deals with a very unusual case, Meredith delves into her family's dirty laundry, and George pours his heart out.

Derek, George, Alex, Burke, Richard, Joe and Walter go on a camping trip. Meanwhile, Meredith assists Mark with gender reassignment surgery, Izzie avoids discussing her grief, Addison works with Callie, and Cristina feels Bailey's wrath.

Sadie manipulates the interns into performing a procedure that goes horribly wrong, Izzie's ghost refuses to leave, and Mark bonds with a girl who's taken responsibility for her sleep-walking father.

It's Valentine's Day and the doctors must treat dozens of injured people after the roof collapses at a popular romantic restaurant; Derek tries to manage his busy schedule as Chief of Surgery; Meredith wrestles with her new duties as the Chief's wife; and Mark and Callie team up to convince Sloane to do the right thing for her baby.

A stampede at a comic book convention leads to an influx of patients.