When Sam is unable to sleep and won't leave the bunker, Dean suggests that they look into the case of a retiree who bashed his head in while yelling that he could hear someone screaming.

When a babysitter is murdered on Valentine's Day and her heart torn out of her chest, the Winchesters learn about it and investigate. They discover that an ancient curse is responsible for the death, and that it's passed on by kissing. To save the next victim, Dean kisses her... marking himself for death.