The CW’s “Supernatural” closed out its ninth season with a powerful — if not altogether surprising — finale on Tuesday night, leaving viewers teetering on the edge of a brutal cliffhanger that will assuredly shatter the show’s status quo when it returns for season ten this fall.

The episode’s final moments (Spoiler Alert if you haven’t watched) saw heroic monster hunter Dean Winchester (Jensen Ackles) — one of the show’s two protagonists — return from death with the signature black eyes of a demon, tragically transforming him into one of the creatures he’s spent his life fighting. His brother Sam (Jared Padalecki), was too busy trying to summon the reinstated King of Hell, Crowley (Mark Sheppard at his scenery-chewing best), in an attempt to save Dean’s life, to realize that the cunning demon was already in the building, ready to welcome Dean into the ranks.

The dramatic...