A Black Day for Hogwarts

NOT ONE OF MY NICE STORIES! HARRY gets killed and comes back to Hogwarts as a ghost... "Nevertheless my boy," Dumbledore said, "Voldemort is still alive." "And why does that concern me?" Harry queried. "I'm not alive anymore." "It might not concern you, but it endangers the whole magical world, and since you're the only one able to defeat him..." Completely AU. ath!Harry etc