Once upon a time, there was a peaceful mountain village. It was blessed with a holy pond, inhabited by a pair of mermaids. Sisters eternal, they loved nothing more than to help the villagers using their great wisdom.
"Obey us in all things, no matter how strange," they said. "What we will ask you to do may alarm you, but it is for your benefit, and your village will prosper." And so it did.
But if that were the end of the tale, you wouldn't be here.