The Lost and the Lurking by Manly Wade Wellman

A Silver John novel.

Apparently he was asked to investigate a town called Wolver. He does. After traveling by a house where a black man is living, he goes in and finds an unfriendly town, and a woman called Tiphaine who presides over it.

He learns a lot of things about the town. It involves books, dust, John's guitar, whether to eat a supper, and more. The black man, named Simon, was a minister, which proves important.

The author's listed in Appendix N for D&D inspiration. This book definitely would be of use to some DMs.