Here Lies Gloria Mundy — Gladys Mitchell

It deals with witchcraft (three witches - Dame Beatrice Lestrange Bradley, the Chaucerian Aunt Eglantine, and the mysterious Gloria Mundy, half her hair red, the other half black, her ancestor burnt as a witch). Gloria Mundy arrives unannounced at the house of her former lover, various accidents happen, and Gloria Mundy's body is found at the dower house - a red wig lying on the corpse.