I like it. I like the vagueness of the threat as well. That'll be good for atmosphere, drama and suspense. Sometimes in horror, the difference between a ghost, a demon and a psychotic human is negligible. Because the monstrosity is not in what they are, but what they do and what they aren't. 

Anyway, is it okay if our characters are slightly creepy themselves? Like if Harold Carter, or someone like Harold Carter, had a daughter and the child saw him eating her mother before he nearly went after her. Such a kid might not be mentally normal after experiencing that. But she wouldn't be one of "them" either.