The villages of Upper and Lower Warden have been feuding since the days of Cromwell and the Civil War, but now the feud has taken a deadly turn. Larry Smith, the star of a horror film titled The House of Satan, based on events centuries ago, is murdered. Smith is the son of the preeminent local family, the Smythe-Websters. His father is the local vicar, his uncle is the lord of the manor and another uncle is the producer of the movie. Some residents of Lower Warden object to the fact that an important piece of local history has been turned into a cheap horror film. Is this enough to kill or is it that there are dark secrets that offer a more serious explanation? When a second member of the Smythe-Websters is killed, Barnaby believes in the latter and looks into the family history to find the solution.