An excellent source book for the Wyrm. Included are the history, goals and the affiliations of the Wyrm. It's machinations and allies and enemies in the mortal world are all chronicled for all to read. The illustrations are very impressionable and can help you envision what the Formori and other denizens of the Wyrm would look like.
By this installment if you want to properly understand what the Wyrm is, the influence it wields and the results it creates.