A New Kind of Evil

"I wasn't choking on food, but a memory, one so dark and so violent that my body was physically rejecting the recollection. Sammy's face was frozen in a look of abject horror, a look I had sworn would never again obstruct his features." Sam and Dean discover that not all evil is supernatural; in fact the darkest evil of them all is of a human nature. Hurt/Sam, Protective/Dean.