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 staff continue to assist those affected by the storm. Meanwhile, Callie makes a bold decision regarding her relationship with Arizona, and tragic news brings the doctors together.
Derek and Meredith adjust to life at home with their newborn and Arizona tries to repair her marriage. Elsewhere, Jackson and Owen clash over financial issues.
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.
Meredith jumps back into work but finds it hard to excel at both motherhood and being a surgeon. Stephanie tries to make a good impression on Jackson's mom, and Jo finds herself overly involved with her new patient. Meanwhile, Callie and Owen deal with an emotional situation regarding a patient.
Derek and Callie work on a brain mapping project, Richard encourages the interns to use his physical condition as a learning tool and after a discussion with Callie, Meredith considers continuing her mother's research. Meanwhile, Shane continues to feel guilty about Heather's death.
It's Halloween and the doctors of Grey Sloan Memorial are hit with a barrage of spooky patients, which affects their own plans and puts one doctor's well-being in jeopardy. Meanwhile, Derek collaborates with Ben on a new surgical technique, and Richard angers Bailey when he asks a second year resident to perform his next surgery.
The issues between Meredith and Cristina hit a boiling point when one of them ultimately betrays the other at the hospital. Derek tells Jackson that he needs to let go and allow the second year doctors to work on his patients, and April and Matthew make a bold decision about their relationship. Meanwhile, Bailey has difficulties with Ben's return.
When an unexpected malpractice suit turns Callie's world upside down, her supportive father arrives and shares an interesting secret with her. Meanwhile, through flashbacks, we learn some surprising details about Callie and Arizona's marriage.
Ben worries that a casual conversation with Derek could potentially cause issues for Bailey, Cristina turns to Shane as tension grows with Meredith, and April's upcoming wedding makes for an uncomfortable situation between Jackson and Stephanie. Meanwhile, Meredith plans a Thanksgiving dinner at her house.
April's sisters arrive to help celebrate April's upcoming nuptials and quickly get on her nerves. Matthew and Jackson are forced to work together when they witness a terrible accident. Callie and Arizona work hard to reestablish their relationship and Cristina is pressured to live stream an upcoming surgery. Meanwhile, a familiar face returns to the hospital.
On the day of April's wedding, the Grey Sloan Memorial doctors are all preoccupied with their own drama. Meredith and Cristina continue to argue about their research and careers, Bailey comes clean to Ben about her feelings regarding him moving back to Seattle, and Shane puts himself in a risky situation.
Meanwhile, Derek gets a phone call that will change his life.
The doctors face the consequences of the events that took place at April's wedding. Meredith feels betrayed when Derek goes back on a promise, Alex is furious after returning to the hospital and hearing the news about his father, and Arizona and Callie decide whether or not to move forward together. Meanwhile, Bailey realizes she was wrong about the motive behind Ben's decision to move back to Seattle.
After an anonymous complaint is issued by one of their own, the hospital implements a non-fraternizing policy causing the couples to panic. Meanwhile, Emma and Owen talk about the future, Cristina and Meredith enjoy a little girl time, and Richard enlists the residents to help research a rare cancer case.
Arizona has a bad day which escalates when she advises one of Callie's patients on a potential double amputation. Derek goes back on a promise to Callie, and Jo and Stephanie come across an abandoned baby outside the hospital. Meanwhile, the doctors deal with the repercussions of the non-fraternization rule, which include meetings with HR and one doctor's suspension.
It's Richard's birthday and Bailey invites him to scrub in on the case of a lifetime. Meredith hires a research assistant to help with her portal vein project. A scorned Callie gives Derek quite the shock. Meanwhile, Shane helps screen candidates for Cristina's clinical trial and meets a young expectant mother who needs his help.
Cristina imagines the two routes her life can take based on one decision she makes. Meanwhile one of the hospital's patients decides whether or not to live.
The hospital gets inundated with flu infected patients, which causes the doctors to slowly fall ill one by one. Derek must fight off the sickness as he prepares to give a speech on brain mapping and the residents place bets on who will fall ill first. Meanwhile, a new doctor at the hospital gives Alex a glimpse into an alternate form of medical practice.
Cristina is nominated for a Harper Avery and although most of her fellow doctors are ecstatic, she won't let herself get too excited. Bailey continues to work on a young boy without an immune system - Alex considers making a change, and Derek and Callie work with a machine that can recognize emotions. Meanwhile, Richard gives the residents a pep talk about the exciting projects going on around the hospital.
Cristina enlists Meredith to help her prepare an acceptance speech for her possible Harper Avery win and while Owen offers to attend the ceremony with her, she insists on going alone. Meanwhile, Derek feels overwhelmed between his responsibilities at home and at the hospital. April and Jackson come to a disagreement on children and religion, and Callie and Arizona try to reconnect in their marriage.
Jackson is given the daunting task of delivering disappointing news to the doctors. Meanwhile, Derek's sister Amelia drops by for a surprise visit, Richard surprises Catherine in Boston and when Bailey gets frustrated by the slow pace of her research, she makes a risky decision.
Cristina looks to Meredith for advice as she assesses her future at the hospital. Derek and Amelia work together on a difficult surgery involving conjoined twins. Meanwhile, Jo is spread too thin when she tries to work on several cases at once and Stephanie realizes the truth about Bailey's bubble boy case.
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.
The doctors of Grey Sloan Memorial Hospital bid an emotional farewell to the beloved Cristina Yang. A possible act of terrorism rocks Seattle and causes chaos at the hospital. Meanwhile, Meredith makes a life changing decision and one doctor receives shocking news.