Help, can't remember the title.
 

There was a horror/suspense novel I read years ago that featured monsters (or deamons or aliens I don't quite remember) that were disguised as everyday people and only a few humans could tell I remember that one of the people was a three eyed Carney who I think could smell them, and another individual who could actually see through their magic or whatever it was. The creatures were extremely tough to kill and I think there was a part where they go back to where one of the characters had disposed of one and find it missing.

I've been trying to find the book but can't remember the title or much else about it if anyone knows it or even thinks they might please let me know.

Twilight Eyes by Dean Koontz?
 

Your description reminds me of Twilight Eyes, especially the carny parts.