The Book of the Dead is a magical book stolen by Marthonis from Marali in 426. It is said that it was thanks to the book that he became a necromancer, and able to create his Bone Lords and Bone Knights.
According to two Bone Lords looking for the lost page on Tholarius during the Sleeping Moon of Year 433, the Book of the Dead contains many existences, or "pages". The book might lose a page when a lost name is uttered and knowledge previously within the book escapes. The existences can have been awakened from the book or not, so it is important to return the knowledge to the book before it takes over a new image. Or at least it is important to Marthonis, of course. The two Bone Lords did not care to explain anything in detail, certain that they would not be understood.
It is not known how the Book of the Dead ended up in Marali. Before Marthonis, the only records that mention the book are extremely old, from a different era of Oberin. Coincidence or not, it is known that is was used by Tholarius and Travis to summon Dominus back, which they did with some help from the witch Sevohabwyn.