A Hearse on May-Day — Gladys Mitchell

Fenella, great-niece to the unorthodox psychoanalyst and sleuth Mrs. Bradley, unwittingly stumbles upon a pagan ritual in the sleepy village of Seven Wells. When the village's pub landlord disappears, Fenella calls on her great aunt's expert advice to help her unravel the developing mysteries. Why was the squire of the village stabbed in the back? And what is the secret of the five skeletons in the crypt?