 In episode 9, an SAS soldier says that Bokken Castle reminds him of  a ghost story about "the end of World War II, and a castle in  Transylvania, and the devil that lived there." This is a reference  to the F. Paul Wilson (qv) novel (and Movie)  _Keep, The (1983)_ (qv). Incidentally, there is a character in the  episode named Paul Wilson.