Cristina, back from her honeymoon trip, searches in vain for Burke; Meredith, Cristina, Izzie and Alex spend their first day as residents with their own groups of interns.
The residents and interns treat the victims of a massive explosion at an apartment building; Mama Burke returns to collect her son's things; Lexie tries to have a heart-to-heart with unwilling Meredith.
George's skill level dazzles the new interns; Meredith halfheartedly helps Lexie with her first emergency patient; Sloan and Richard attempt a radical new surgery to save a woman's ability to speak; George tells Callie of his past indiscretion with Izzie.
The chief's wife rushes their niece to Seattle Grace; Izzie gets an unexpected reaction when she reveals her feelings about George to a mutual friend; Derek shows Cristina how to be a better teaching resident; Norman misdiagnoses a problem.
Halloween is full of surprises for the doctors of Seattle Grace; Alex receives an unexpected visit from a former patient; Meredith thinks her mother's ashes are haunting her; a surgeon Cristina admires snubs her.
The chief has a gentlemen's evening with his fellow surgeons; Cristina and Izzie find themselves competing for the same surgeries and the favor of the doctors performing them; Meredith tends to the survivor of a sky-diving accident.
George and Izzie test their romantic chemistry; Derek asks for more than a physical connection with Meredith; Mark develops a crush on a fellow surgeon; Callie finds her role as chief resident jeopardized.
Teenagers fill the ER after a school-bus crash; Bailey treats a patient who was her high-school crush; Derek goes on a date with a fellow doctor; Thatcher enters the ER looking for Meredith.
An ambulance crash endangers the lives of the paramedics involved; Bailey treats a patient who refuses her help; Ava returns for Alex and meets his other girlfriend.
Meredith furiously works to save the life of a paramedic trapped in an ambulance; Lexie holds a patient's life in her hands; Derek must rely on a nurse's help to save a patient; Bailey struggles to balance her personal life with work.
Bailey's family faces a medical trauma just as her marriage falls apart; George's mother makes a surprise visit; a faith healer challenges Erica and Alex's belief in traditional medicine; Derek must deal with the aftermath of his kiss with Rose.
Six weeks after Derek and Meredith ended their relationship, Meredith, Alex, Izzie and Cristina compete in a surgical contest, with Bailey serving as judge; George and Lexie adjust to their new, squalid apartment; Callie finds a friend in Erica.
Addison returns to Seattle Grace to perform an operation and is surprised by all the changes in the lives of her former co-workers; Derek and Meredith's clinical trial has its first patient; Rebecca returns with shocking news for Alex.
The nurses' complaints about Mark Sloan's trysts result in a date-and-tell policy; Cristina is forced to face her feelings for Burke; Meredith and Derek admit a veteran into their clinical trial.
Dr. Wyatt refuses to let Meredith give up on therapy; Alex learns the truth about Rebecca's medical condition; the chief insists Erica perform a risky surgery on his mentor.
Meredith and Derek get one last shot at success in their clinical trial; the surgeons work together to free a boy from a block of cement; Izzie helps Alex care for Rebecca; Lexie uncovers critical information about George's status as an intern.
Meredith and Derek get one last shot at success in their clinical trial; the surgeons work together to free a boy from a block of cement; Izzie helps Alex care for Rebecca; Lexie uncovers critical information about George's status as an intern.