When the time-gun boomed from Edinburgh Castle, Bobby gave a startled yelp. He was only a little country dog—the very youngest and smallest and shaggiest of Skye terriers—bred on a heathery slope of the Pentland hills, where the loudest sound was the bark of a collie or the tinkle of a sheep-bell. That morning he had come to the weekly market with Auld Jock, a farm laborer, and the Grassmarket of the Scottish capital lay in the narrow valley at the southern base of Castle Crag. Two hundred feet above it the time-gun was mounted in the half-moon battery on an overhanging, crescent-shaped ledge of rock. In any part of the city the report of the one-o'clock gun was sufficiently alarming, but in the Grassmarket it was an earth-rending explosion directly overhead.