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.

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.