"GREY'S ANATOMY - ""Scars and Souvenirs"" - The race for chief heats up after a new competitor enters the fray, tensions escalate between Izzie and George, and Callie must reveal a big secret. Meanwhile, Derek treats a patient near and dear to him, while Alex continues his work with Jane Doe, on ""Grey's Anatomy,"" THURSDAY, MARCH 15 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/RON TOM)KATHERINE HEIGL, JAMES PICKENS, JR., SARA RAMIREZ"