The Dunwich Horror tells of a family in a remote village that called down Yog-Sothoth. The deformed son Wilbur and his unseen twin, growing invisibly and filling a barn, come to threaten the village.
It is a rare "fighting back" structure, in which scholars of Miskatonic University answer with rites from the Necronomicon, and it has a comparatively clear ending for the Mythos.