From the Publisher's Website
There are those within the Order of Hermes who transmit secrets of magic incomprehensible to outsiders. Pre-eminent among them are the four Mystery Cult Houses, gatherings of magi Initiated into the same Mysteries. This book details the Mystery Cults, including full details of their Inner Mysteries.
* House Bjornaer venerates animal ancestors, and strives to perfect the form. Their Mysteries enhance the heartbeast, ultimately allowing the magus to unlock mythic forms.
* House Criamon follow ancient teachings and seek escape from time itself. The many paths that they walk to this end grant powers that can include immortality.
* House Merinita move among the faeries, ultimately joining them. Their spells can draw on faerie glamour, awaken the fay slumbering around them, or inflict curses on those who break their promises.
* House Verditius crafts the greatest items, putting a little of themselves into their finest creations. Pride in their creations is often their downfall, and these magi are terribly prone to the most deadly sin.