Owen puts the residents through a rigorous trauma certification drill; Cristina is left alone to monitor an ill lung transplant patient.

Thatcher Grey, Meredith and Lexie's father, returns to Seattle Grace with stomach pains and a new, twenty-something tattooed girlfriend, Danielle. Meanwhile, Alex clashes with the new OB, Dr. Lucy Fields, over a patient and Mark places Jackson on his service in exchange for information on Lexie.

The doctors become nostalgic when George O'Malley's mother, Louise, returns to Seattle Grace for medical help after a botched surgery at a neighboring hospital; the residents are inspired by a medical miracle when they witness a harvested heart that continues to beat outside the body; a new pediatric fellow excites Arizona and makes Alex feel threatened; Jackson lets his suspicions about Mark and Lexie interfere with his work; and Henry and Teddy have their first marital fight when he expresses interest in pursuing medical school

Amelia arrives at Seattle Grace to beg Derek to help with the gliosarcoma case; Cristina and Owen have heated arguments during marriage counseling; Alex realizes he needs to improve his people skills in order to be a good doctor.

Aware that Derek might never operate again, Meredith stops talking about the surgeries she's performing. Meanwhile, Richard calls on Dr. Catherine Avery to help him perform a complicated procedure, as things continue to heat up between Jackson and April; and Arizona's struggle to accept her fate forces Callie and Alex to face their guilt.

Bailey puts her wedding day on hold and continues her efforts to save Adele's life, Cristina and Owen remain undecided about their pending divorce, while Arizona and Callie try to get their spark back. Meanwhile, the hospital becomes inundated with a group of bikers after a horrible accident.

As word of Seattle Grace's financial trouble spreads, Catherine encourages Jackson to move to Boston, and the interns fear they might lose their jobs. Meanwhile, the doctors meet with a potential investor in a last-ditch effort to save the hospital, and Alex impresses Jo while caring for a patient.

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.

With Derek away, Meredith spends time with Amelia and finds out her true feelings about her time in Seattle. Bailey deals with the ramifications of her actions and Callie receives devastating news. Meanwhile, the residents panic after hearing that one of them will be fired

Owen becomes invested in a patient when he realizes she may have served in the military, April’s mother pays her daughter a visit and bonds with Jackson, and Derek plans a family dinner. Meanwhile, a patient’s diagnosis causes Bailey to reconsider her own health issues and Dr. Herman drops a bombshell on Arizona

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.

A small plane crash in Seattle causes multiple casualties and brings back horrible memories for the doctors, especially Meredith and Arizona. Meanwhile, friction between Owen and Amelia makes for an uncomfortable working situation for Stephanie.

Owen suggests the interns learn a vital lesson on how to break bad news to patients’ families, and Arizona’s 90-year-old patient reassures her that she’s destined to find love again. Meanwhile, the sisters completely forget about the dinner party they’re hosting for everyone.

Meredith, Bailey, Jackson, Callie and Jo travel to a military hospital to perform an extraordinary and extremely risky surgery on a veteran with an advanced tumor. Meanwhile back at Grey Sloan, Andrew is tired of being Maggie’s worst kept secret; Ben makes an impulsive surgical decision; and a team of cheerleaders wreak havoc in the ER.

Miranda continues to deal with the aftermath of Ben's reckless decision and forms an advisory committee to recommend proper disciplinary action against him. Meanwhile, April and Jackson try to put their differences aside for the sake of their baby, and Arizona makes a decision that could affect her relationship with Callie forever.

The arrival of a new consultant puts all of the doctors on edge, especially once she starts stepping on toes in the OR. Amelia and Owen bring their personal problems into the hospital, while April explores some uncharted territory.

Diane Pierce returns to Grey Sloan, but Maggie is still in the dark as to why she’s really there. Owen and Amelia hash out their problems as they work a trauma case together, and Bailey tries to mend her relationship with Richard.