The residents choose their future positions; Mark admits to Derek that he still has feelings for Lexie; Arizona encourages her friend to have surgery.

The residents travel to San Francisco for the oral boards; sparks fly when Richard and Catherine (Debbie Allen) bump into each other at a hotel; Alex feels guilty about being away from the hospital.

Cristina makes Owen tell her about the intimate details of his affair; Mark takes his authority very seriously when he steps in as chief for the day.

Derek asks Meredith to work with him in neuro again; Catherine Avery (Debbie Allen) comes back to Seattle Grace and takes an interest in Richard; Cristina becomes increasingly suspicious of Owen; Morgan may be falling for Alex.

Amelia arrives at Seattle Grace to beg Derek to help with the gliosarcoma case; Cristina and Owen have heated arguments during marriage counseling; Alex realizes he needs to improve his people skills in order to be a good doctor.

Meredith dreams of what her life would have been if her mother had been healthy.

Teddy puts her husband's life in the hands of her peers; Meredith and Derek receive news about Zola; and Meredith and Alex are involved in a life-threatening situation tending to a sick newborn.

Arizona and Mark have finally become friends, but that proves more annoying than helpful to Callie.

A stampede at a comic book convention; Mark continues to make life difficult for Jackson; Ben returns to find Bailey has moved on.

Meredith faces the consequences of tampering with Derek's clinical trial.