An opening that features the two main characters playing practical jokes on one another is followed by a night of heavy rain and fearful talk of Indian attack and The Black Dog, the latest fearsome-fantastic rumored to stalk the wilderness and a possible stand-in for Cerberus. On September 21, the first day of autumn, Mason & Dixon pass over South Mountain on their way toward Antietam Creek. There, they tour a cave system with spectacular formations and some ancient and undecipherable writings that produce profoundly different reactions in the polar temperaments of the surveyors.