Cursed by lightning

Sam, Dean, and Cas are at a cafe, discussing there next hunt. When a girl runs in and sits in their booth with them. With there premission she stays but Castiel won't stop staring at her. Though all is calm until the guy turns out to be a demon that killed Scarlet's (The girl) sister. (O/c x Dean) [sucky summary I know but please read, Stories not that bad]