RUFFLES AND DRUMS "Could Betty Cavanna ever disappoint her faithful fol- lowing? No way. Sixteen-year-old Sarah Kent witnesses the occurrence at the 'rude bridge' at Concord, Massa- chusetts, in April, 1775. James Butler, a British soldier, is wounded and taken in by Sarah's parents, much against the girl's will, since a shot from his musket has killed her dog. Ms. Cavanna has re-created the p…