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.