The Dunwich Romance by Edward Lee
It's a hot day in Virginia during the Great Depression, when a bus breaks down on a lonely backwoods road. The passengers are told the repairs will take till tomorrow, so... What will they do tonight? Good fortune strikes! Just down the road, there's a carnival! The last man off is a writer and sightseer from Rhode Island, a man named Howard Phillips Lovecraft...
O'SLAUGHNASSEY'S TRAVELLING SHOW! RIDES! CONCESSIONS! ODDITIES OF NATURE! COME ONE, COME ALL!
A genuine mermaid! A living cadaver! A man with three eyes! There's even a girl with hands for feet! Howard knows that such "spectacles" are all too often frauds, but what Howard doesn't realize is this: the carnival's frolicky fun will quickly degrade into a waking nightmare of unspeakable carnal depravity and sick-in-the-head violence beyond anything he could ever conceive. And when he finally flees the wretched scene... Something awaits him a thousand times worse.