Amrapali Ambegaokar

Meredith, Cristina, Izzie and Alex spend their first day as residents with their own interns, including George, repeating his internship after failing his exams, and Meredith's half-sister. Cristina searches for Burke, who is nowhere to be found and Richard resumes his position as chief of surgery.

Meredith and Derek rediscover the morning-after side of their relationship; the chief learns the hospital has slipped in the national rankings.

The residents and interns treat the victims of a massive explosion at an apartment building, while Alex investigates the cause of the accident.

George and Izzie's romantic chemistry is put to the test. Mark develops a crush on a fellow surgeon. Callie's role as chief resident is in jeopardy.

The new interns are dazzled by the skill level of fellow intern George, while Lexie helps keep his "repeater" status a secret; Meredith half-heartedly helps Lexie with her first emergency patient.

Major Owen Hunt returns to be the head of ER trauma; Meredith finds an old doll her mother gave her when she was 5.