The residents and interns treat the victims of a massive explosion at an apartment building, while Alex investigates the cause of the accident, Mama Burke returns to collect her son's things just as Cristina trades her wedding presents in exchange for surgeries, Lexie tries to have a heart-to-heart with an unwilling Meredith, and while Callie is overwhelmed with her duties as Chief Resident, Bailey searches for an outlet for her pent-up leadership skills.