S4, E1: Having just returned from her honeymoon with Meredith, Cristina searches for Burke, but he's nowhere to be found. Meredith, Cristina, Izzie and Alex spend their first day as residents with their own groups of interns - among the interns are George, repeating his intern year after failing his exams, and Lexie Grey, Meredith's half-sister whom she has never met. Now that Derek's relationship with Meredith has reached an emotional impasse, he looks to his fellow doctors for friendship; Bailey wrestles with her place within the hospital now that her former interns report to new Chief Resident, Callie; Richard resumes his position as Chief of Surgery.