Supernatural (TV series)/Recap/S02/E13 Houses of the Holy

Season 2, Episode 13:

The Houses of the Holy
Sam and Dean investigate murders in which the killer claim an angel told them to kill the victims. As each victim was unknown to each murder, Sam and Dean suspect something less celestial and more spooky is going on.

Tropes

 * Hourglass Plot -- In the beginning Dean is bitterly stubborn on the point that angels (or anything pure and good) could never exist in such a Crapsack World, while Sam is open and hopeful about possibly finding an angel. By the end, Sam is disillusioned upon finding that the so-called angel was just the ghost of a fanatical priest while Dean witnessed a minor miracle and therefore became a bit more open-minded about the possibility of good in the world.
 * Mission from God -- each murder claims an angel told them to kill their victim.
 * Nay Theist -- Dean claims not to believe in God or angels because the world wouldn't be as messed up if they existed.