The Old Gods Waken by Manly Wade Wellman

In the Appalachian mountains, a wandering balladeer becomes entangled when two urbane outsiders attempt to revive ancient druidic powers at a prehistoric mound, stirring forces older than the hills. Armed with folk wisdom, faith, and the music of his silver-stringed guitar, he rallies local allies to protect a mountain family and confront eldritch presences transplanted from Old World myth into New World soil. As omens mount and forbidden rites begin, he navigates superstition and scholarship alike to keep the old powers from waking fully.

Purchase from Bookshop.org