While Meredith faces the repercussions of messing with the medical trial, April tries to step up as chief resident; Cristina and Owen disagree.
Meredith and Derek's relationship concerns Zola's adoption counselor; Alex notices he has become an outcast; Cristina makes a difficult decision.
The chief makes a decision that shocks everyone at Seattle Grace; Owen and Cristina attempt to find normalcy; April struggles in her new role; the fifth-year residents receive their first solo surgery assignments.
A stampede at a comic book convention leads to an influx of colorful characters in the ER; Mark continues to make life difficult for Jackson; Ben returns and realizes Bailey has moved on.
The residents try to impress Jackson's mother, Catherine Avery, when she comes to Seattle Grace to perform a groundbreaking surgery; Alex and Arizona encounter a familiar face in the ER; Bailey makes a choice about her love life.
Through Lexie, Meredith tries to get Derek interested in a patient's rare brain tumor; Callie ends up being annoyed when Mark and Arizona finally form a friendship; Teddy and Alex look into alternative surgeries for a superficial patient.
Owen organizes a baseball game against Seattle Presbyterian; Lexie is unable to control her emotions when she sees Mark with a new woman; Alex fights for Zola; Richard talks to Meredith and Bailey about their feud.
George O'Malley's mother comes to Seattle Grace for help after another hospital botches her surgery; a medical miracle inspires the residents; Jackson's suspicions about Mark and Lexie interfere with work.
Teddy is called away on another case, as Henry is brought in for emergency surgery; Derek and Meredith finally receive news about Zola; a patient experiences complications after surgery.
The eldest daughter of a family involved in a car crash must make a difficult decision; Teddy asks Cristina to help with an O.R. patient; Lexie works with Mark's new girlfriend during a surgery.
The doctors form two teams to operate on conjoined twins; Bailey uses Meredith as a buffer between her and Ben; Alex learns a tough lesson; Teddy asks Cristina about Henry's surgery.
Richard's 10,000th surgery is a liver transplant for two sisters; Derek and Lexie take on a case that had been declared inoperable; Teddy and Cristina try to swipe a case from Alex and Dr. McQueen; Meredith tries to choose a specialty.
Meredith dreams of what her life would have been if her mother had been healthy.
Lexie watches Zola as Meredith and Derek try to have a night to themselves for Valentine's Day; Callie surprises Arizona with a romantic evening; Ben tries to prove that he knows Bailey better than she thinks.
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.
As Adele's condition deteriorates, Richard considers making a change; an explosion at a coffee shop results in a busy ER; Callie helps Meredith study; Lexie helps Alex and Arizona care for an intern's premature baby.
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.
An escaped lion puts lives and relationships in danger; Lexie hears Mark talking about moving in with Julia; Teddy begins to come to terms with Henry's death; Callie asks Arizona about her past relationships.
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; Arizona, Callie and Bailey plan special night for Teddy.
The doctors treat a Jane Doe who turns out to be the subject of a nationally followed case; the residents begin their interviews for post-residency positions; Richard faces a disturbing realization while visiting Adele.
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 when Tommy's health takes a turn for the worse.
The residents agonize over their upcoming exam results; Arizona's childhood friend needs medical help; the doctors try to help a patient who is missing one third of his skull; Julia wants to start a family with Mark.
The residents choose their future positions; Mark admits to Derek that he still has feelings for Lexie; Arizona encourages her friend to have surgery.