From the back of the book: "Three struggles across time and space against the Great Old One, Hastur" This book for Call of Cthulhu contains three linked scenarios, each set in a different time and place. 'Adventus Regis' takes place in ancient Rome and makes use of the 'Cthulhu Invictus' Monograph. 'Herald of the Yellow King' is a Dark Ages scenario, making use of 'Cthulhu Dark Ages'. 'Heir to Carcosa' takes place in the near future and is best played with the 'End Times' Monograph. There are also chapters giving further information on Hastur and his followers in these time periods.