The Watcher by the Threshold

Five stories of the Scottish moors and the far places of the empire, in which something older than the men in them is still active: a remnant of the Picts in the hills, a dream of islands in the west, a devil in a Border house. Buchan wrote them before The Thirty-Nine Steps, and they are the seed of everything unsettling in his later work. The title story is his best piece of pure fear.