When Janice and Tommy Brooks are invited to visit their Aunt Annabelle and her son Hubert at their new house in Maine near the Canadian border, they expect to have a wonderful summer. What they don't expect is to hear galloping hoofbeats in a rock or to see an old man with a flickering light appear out of nowhere in the middle of a midnight storm. They don't expect to have a guest who creeps around the top floor when he thinks the family is asleep. And they never dream that they might get involved in the dangerous adventures of the Border Patrol!These puzzling and frightening events increase the general feeling of mystery that surrounds Mountain View House. Aunt Annabelle bought it to run as a guest house, but both local visitors and tourists keep away. The children have to find the explanation for these strange happenings before Fall, or Aunt Annabelle will have to give up her dream of running a guest house!