Introduction: A horror stalks the night, collecting its grim toll.Elspeth MacAdams and Gregor Lythgoe are detectives, part of the secretive Special Investigations unit. Experts in the strange, occult and supernatural, they arrive on the tiny Scottish island of Raasay to investigate a grisly murder.Darkness lurks at the heart of the tiny rural community. Soon they find themselves battling to stop unnatural rites and ancient evils. One again they find themselves the thin blue line standing before the darkness.Can they stop the looming evil in time? Before it adds them to The Pillar of Horns....