“That’s a beacon-holder,” Mr. Dwight told her. “In the good old days of the Border Wars, this castle used to be a station in the chain of signal fires. They fastened a bundle of fagots into that frame and set them on fire, and the chief in the castle over there on one of those purple islands, and the clan gathered on the slope of Ben Cruachan, that highest peak up at the head of the loch, saw the fire, and knew what it meant.”