The Company She Kept — Marjorie Eccles

When the half-dressed body of Angie Robinson is found strangled in the lay-by on a lonely moorland road, it seems that her murder is the result of a random attack, for Angie has led a blameless life, with no interests other than her untiring support for the local women's hospital.
But there are too many apparently unrelated elements in the case for DCI Gil Mayo to be satisfied with that explanation. For one thing, an anonymous letter has been sent to the police with hints of a long-ago murder and ancient sacrificial rites. Then there is the old house, Flowerdew, which exerts a strange but compelling fascination. And what of Flowerdew's eccentric but endearing owner, Kitty Wilbraham, a former archaeologist who had worked on the ruins of ancient Carthage? Kitty always had a group of younger men and women drifting through the house; what roles could they have played, and where is Kitty now?
It is not until another body is discovered that Mayo, with his new Sergeant, Abigail Moon, is finally able to link the two murders together and arrive at a solution that is as unexpected and bizarre as any in his career.