A few months ago, a cult rose up out of no where. It was believed to link directly to demons, or more accurately, the Devil. Cultists believed that whoever had wronged them would be severely punished, sacrificed. That the Devil, once known for being an angel, would rise again to claim what he had so longed for. That mankind would finally be corrupt and killed for all the wrongs they had committed.
And well... They weren't necessarily wrong.
Before long, cult members started going missing, disappearing into thin air. The only evidence left behind were summoning circles that seemed to let off a black smoke.
It happened more and more regularly, and that only seemed to attract more people to the cult. The more people it attracted, the more people disappeared. The more people disappeared, the more people grew curious. Investigators were sent in as spies to investigate, but they disappeared too.
Two months after the start of the cult, and they began to send out preachers. People to testify of the coming of the end, the beginning of the apocalypse, and the mass murder of the unworthy.
The cult members were soon to be arrested on sight, but they would not stop preaching. They would not stop praising their lord of vengeance and death.
Finally, after plenty of begging and backlash from reporters and citizens, the news companies were permitted one interview with an arrested preacher. The words that were spoken shook most everyone to the core.
"I will tell you all this one thing, and this one thing alone. The disappeared are not dead, they are saved. Our lord blessed them with his children's blood, and turned them into the bringers of death that will rid this place of filthy, disgusting humans. One month, you have one month to prepare yourself. The bringers of death will kill you all, and the Lord and his demon children will reclaim the Earth as theirs, as it should have been! Kill you all, kill you all!" He started laughing maniacally and lashing out at the officers and reporters, never once stopping, even though he was being beat in an attempt to restrain him. It was like he no longer felt pain.
Violet, a recent high school graduate, looked at the new TV in horror as the screen went blank. She had just moved into her college dorm, away from her family. She began to panic, feeling with all her being that something would be coming soon. Though her mind wanted to deny it, she wasn't wrong. He hadn't lied.
The day before the claimed month arrived, the remainder of the cult followers disappeared, even the ones locked up. 
And the next day... Everything changed. 
The monsters came from the shadows, and they killed.