The Cats of Ulthar is a short story written by H.P. Lovecraft and published in 1920. It concerns the village of Ulthar, a primeval collection of hovels located somewhere in the distant past (or maybe the future, you never really know with Lovecraft), which has a law that no man may kill a cat. This law came out of an incident involving an old couple that were known for killing the local cats in some suitably gruesome fashion that half the village could hear the death throes of the poor beasts. Since PETA wasn't a thing in the dark ages but the bystander effect was this situation persisted for a long time.
That is until some dark skinned folks with pictures depicting fantastic creatures with the bodies of men and the heads of beasts and fowls on their wagons showed up to trade. Among them was a young orphaned boy who's only family was a small black cat. You can probably guess what happened next. When the kid's cat disappeared the boy wept and searched until someone informed him of his pets probable fate. Instead of more crying the child became very quiet. Then he began to pray in an unknown language. What he said is not remember by the villagers and not just because none of them could understand it but because the clouds above them had begun to take on strange shapes of half human creatures.
That night the travelers left never to be seen again and the next morning Ulthar's cat population was absent. Some said it was the travelers, others the creepy old couple, and one kid claimed he'd seen all of the village cats marching around the old couple's cottage like some freaking pagan ceremony. The child was of course dismissed completely. The very next day the cats returned fat and happy. When the couple's absence was noted a handful of brave villagers investigated to find nothing less than two human skeletons picked clean and "a number of singular beetles crawling in the shadowy corners." I can't help but wonder what made the beetles singular if there were several of them.
As far as stories go this one is almost too straight forward. Cruel old people meet a terrible fate facilitated by a foreign deity of unknowable alignment. Only that last part really strays from the format of a typical Grimm's Tale and even then only barely. If you like cats or just want to read an old creepy tale for the next five minutes then give it a look.
RUST IS FOR THE WEAK