1x18 Something Wicked

On a tip from their father, Sam and Dean head to Fitchburg, Wisconsin, to investigate a case in which children have fallen into comas. They soon discover that the creature responsible is a vampiric witch known as a shtriga, which is stealing life force from the kids. Dean reveals to Sam that their father had previously attempted to kill the creature when they were young, and that Dean's recklessness almost cost Sam his life and allowed the shtriga to escape. After they learn that the owner of the motel they are staying at has a young child that has also fallen victim to the creature, they use the boy's older brother as bait to lure the shtriga. Sam and Dean kill it, and all the children recover.