Invisible Sun Book MEven its name is a secret Some say it comes from the Sodality of Vryn, which identifies thirteen currents of magic and gives each a letter designationM is the 13th and most powerful. Others say the title refers to the original writer of the book, while still others believe it stands for mystery, orperhaps most simply and obviouslymagic. Whatever the source of its name, Book M is one of the rarest and most sought after grimoires. Its whispered to