Following the storm, a mudslide injures first responders and citizens; Meredith faces a decision that will impact a loved one; Callie is rocked by Arizona's infidelity.
Callie makes a decision about her relationship; the doctors receive devastating news.
Derek and Meredith adjust to life at home with their newborn; Arizona tries to repair her marriage; Jackson and Owen clash over financial issues.
The doctors put together a fundraising gala; Bailey must face several difficult patients; Shane and Stephanie take care of the busy ER on their own; Alex opens up to Jo.
Meredith struggles to balance her roles as a surgeon and a mother when she returns to work; Stephanie tries to impress Jackson's mother; Jo becomes overly involved with a patient.
Callie and Derek collaborate on a brain mapping project; Meredith thinks about continuing her mom's research; Shane's guilt persists.
Costumed patients create a challenge for the doctors; Derek and Ben work on a new surgical technique; Richard asks a resident to perform his next surgery, angering Bailey.
A betrayal intensifies the issues between Cristina and Meredith; Matthew and April make a decision about their relationship; Bailey faces difficulties with Ben's return.
As Callie is faced with a malpractice suit, her supportive father (Hector Elizondo) visits and shares a secret; past details about Callie and Arizona's marriage are revealed.
Ben worries that an innocent conversation with Derek could end up causing problems for Bailey; Cristina turns to Shane as tension with Meredith increases; April's upcoming wedding creates an uncomfortable situation for Stephanie and Jackson.
April's visiting sisters get on her nerves; when Matthew and Jackson witness an accident, they must work together; Callie and Arizona work on their relationship.
Meredith and Cristina bicker about their careers; Bailey talks to Ben about him moving back to Seattle; Shane puts himself in a risky situation; Derek receives a life-changing phone call.
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.
Couples panic when the hospital announces a nonfraternization policy; Owen and Emma discuss the future; Meredith and Cristina have some girl time; Richard asks the residents for help with a rare cancer case.
Arizona's bad day escalates when she advises a patient on a potential double amputation; Derek breaks a promise; Stephanie and Jo find an abandoned baby; the nonfraternization rule leads to a suspension.
Bailey asks Richard to join her on the case of a lifetime; Meredith decides to hire a research assistant; Callie shocks Derek; a young pregnant woman (Keke Palmer) needs Shane's help.
Cristina thinks about her future; a patient decides whether to live or not.
The doctors are exposed to flu-infected patients; Derek prepares to give a speech; a new doctor gives Alex a glimpse into an alternative medical practice.
Cristina won't let herself get excited when she is nominated for a Harper Avery award; Alex thinks about making a change; Callie and Derek work with a machine that recognizes emotions.
Meredith helps Cristina draft an acceptance speech; Derek feels the weight of his responsibilities; April and Jackson are at odds about children and religion; Callie and Arizona try to reconnect.
Jackson must deliver bad news to the doctors; Derek's sister visits; Richard surprises Catherine in Boston; Bailey makes a risky decision about her research.
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.
Meredith learns Amelia's true feelings about Seattle; Bailey deals with the consequences of her actions; Callie receives terrible news; news of a firing causes panic among the residents.