George and Derek work together, Denny still doesn't have a heart, and Meredith gets paired with Callie. A 12-week pregnant girl dies in the O.R. and her parents try to keep the baby alive. This causes tension between Derek and Addison. One doctor's overreaction unites two bickering patients. Finn is still treating Doc for medical problems.

Meredith works furiously to save a paramedic trapped in an ambulance; Lexie holds the life of a patient in her hands; Derek must rely on a nurse to save a patient; Bailey struggles to balance her personal life with her work.

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.

The doctors split into teams for a risky surgery involving conjoined twins; Bailey recruits Meredith to be a buffer between her and Ben when he puts pressure on moving their relationship to a more serious level; Richard teaches Alex a tough lesson in the OR; meanwhile Teddy questions Cristina about what exactly happened to Henry during his surgery.

A lion breaks loose in Seattle, leaving a couple's lives and relationship at risk; Lexie overhears Mark's discussion about moving in with Julia; Teddy begins to take steps towards coming to terms with Henry's death; Callie grills Arizona on her past lovers; and Alex requests to be taken off Morgan's preemie case when she becomes too dependent on him. Meanwhile, Meredith tries to be a support for Cristina as the tension between her and Owen hits a boiling point.

After eight years of practice, the residents head to San Francisco for their oral boards; sparks fly between Catherine and Richard when they bump into each other at the hotel; Bailey intervenes after Owen and Teddy get into a heated argument about their young car crash patient; and Mark tries to recruit Lexie for one of his cases. Meanwhile, Alex feels guilty for being away from the hospital when Tommy's health begins to fail.

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.

Cristina and Owen continue to figure out their relationship amidst the pending lawsuit; and Bailey argues with Ben over plans for their upcoming nuptials. Meanwhile, Callie recruits Jackson to help find a solution to Derek's hand, but he is preoccupied by a shocking situation with April.

Meredith, Derek, Cristina and Arizona receive big news regarding the plane crash lawsuit, Richard avoids Catherine's romantic advances and Jackson takes on one of Mark Sloan's old patients. Meanwhile, Derek begins recovery on his hand.

The Seattle Grace doctors are on edge when a new medical professional enters the hospital; Arizona struggles with the emotional and physical pain of a phantom limb; and while battling pregnancy hormones, an overly-emotional Meredith is confronted with her worst fear.

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 Hospital prepare for a super storm heading towards Seattle. Owen's desire to be a parent gets stronger as he becomes closer to Ethan. One wrong move puts the lives of Meredith and her baby in jeopardy. Meanwhile, Jo looks to Alex for help in a moment of crisis, and one doctor gets the shock of her 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.

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.

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

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.

Jo finally faces her estranged, abusive husband Paul Stadler, while Grey Sloan continues to work with the FBI after a hacker has compromised the hospital’s computer system.