I read a story many years ago that I think was written by Harlan Ellison, which takes place in the 70's and told from the vantage point of a young man who is pursuing a woman who is part of a group/commune.
They move to LA and the group begins doing odd things and anoint the young man as the interface to the outer world, given he is the "straightest" one. Eventually things devolve until the protagonist discovers that in the basement of the building there is swirling water and the girl and her companions have become werewolves or vampires.