Showing Wildfire at Midnight by Mary Stewart

Midnight on Skye: a young crofter's daughter is cruelly and ritually murdered on the bleak Scottish mountainside. Very soon Gianetta Brooke, a guest at the deceptively idyllic Camasunary Hotel nearby, finds herself tangled in a web of rising fear and suspicion. When she discovers that her ex-husband has booked into the same hotel, the peaceful holiday for which she had hoped takes on quite another complexion.