Death of a Fool (Roderick Alleyn Series #19) in Bloomington, MN

The village of South Mardian likes the old ways. This may be 1957, but South M. still features a blacksmith, a village idiot, and an elaborate fertility ritual performed at the winter solstice. There's squabbling, of course, and things come to a head when one of the ritual's main players is found be-headed, everything north of his neck having been neatly lopped off by a ritual sword.