I Will Follow You Into the Dark

After learning at a deposition that more of his patients have died than survived, Derek decides to quit, even as Meredith refuses to give up on him. Meanwhile Bailey and the Chief continue to bicker over her peds fellowship -- until Adele steps in to mediate -- and Izzie's interns discover something unsettling on a "patient x," unaware that the charts they're looking at are actually Izzie's.