The plot would involve a twist in history where a plague struck humanity in 1840 bad enough to nearly wipe out the species. Within 5 years, only 500,000 humans remain. What no one knows is that the creatures of our nightmares have been living in secret, waiting for an opportunity to rise.  Vampires, werewolves and other supernatural monsters came out from the shadows, outnumbering the humans by thousands. The remaining humans panicked and began preparations to defend themselves from these creatures, developing weapons as fast as they could and preparing for war. Vampires outnumbered humans to the point of being able to take full control, using some human as cattle as they occupied noble houses. Werewolves were also now free to come out in packs and hunt humans without the stress of revealing their existence. In this world, humans would have to battle to survive in a new world unlike their old one where they were the bottom of the food chain.