What if Fright Night happened to you?
So you're in your house one night, doing whatever, and you spot movement out the window. You look outside and see that someone is moving into the house next to you. Two men are moving a coffin into the basement. This rouses your suspicion.
People start disappearing. Then one night, you see the neighbor with fangs about to kill a woman he has seduced. He sees you and closes the blinds, but you are sure he is a vampire, and he knows you know this.
What do you do?