"The Church in High Street"

by Ramsey Campbell

originally published  Dark Mind, Dark Heart, Arkham House, 1962

The unnamed narrator goes to see his friend Albert Young, hoping to pick up some work, in a decaying, ancient English town called Temphill.  Temphill and its environs are old, run down, gray and basically icky.  

Albert Young isn't home.  In fact, his door is open and covered in cobwebs - generally not a good sign. A mysterious neighbor, John Clothier, drops some ominous hints and then drops the whole thing.  Leaving the narrator to poke around Young's abandoned house.  He finds some notes and a diary and, in appropriate Cthulhu-story fashion, sits down to read them.  

It seems Young, who was researching a book on witchcraft, had discovered that an old, abandoned church in the town was not so abandoned, and in fact is actively haunted by beings called "the herd" who can breach space and time.

Naturally, the narrator heads right over there - at night, of course.  He encounters visions of other worlds and possibly is affected by "the herd".  He flees the church and passes out.  He is rescued.  But now finds himself drawn to return to the church.

This story, per Campell, was rewritten by August Derleth.  It's a pretty minor tale, but there are hints of the writer Campbell will grow into in the atmosphere and some genuinely unearthly implications.  An inauspicious debut.