The Overseer's book is found on the floor where The Overseer used to be after having it create an abyssal bludgeon. Doing so will initiate dialogue in which the Overseer claims he required the teleportation energy produced from the Sire's body parts to leave the Abyssal Nexus.
Once the Overseer leaves, the book remains on the ground, and is required to create additional bludgeons by using the three pieces (bludgeon axon, bludgeon claw, and bludgeon spine) on the book. It can be stored in a POH bookcase.
Although time does not pass in the Abyss at the same rate that it passes elsewhere, I have been imprisoned for an unimaginably long time, since the days when the gods fought for dominion of the mortal realm.
I leave this book as a token of fair trade to the human who has given me the wherewithal to escape from the Abyss. By absorbing power from an Abyssal Sire's spine, claw and axon, I am able to break free of my prison.
During the wars of the gods, all sought allies in every realm they could reach. I broke into the Abyss in the hope that the creatures here could be turned to our cause, but found myself trapped and unable to escape, while the God Wars continued without me. But now that I am free, I shall not be so easily imprisoned again.
The human who brought me the means of escape did not fully understand my purpose; I merely promised to construct a weapon for him using the component parts of the Abyssal Sires.
Nevertheless, I am bound by my word and constructed the weapon.
I have now imbued into this book the power required to construct such weapons. The human may create Abyssal Bludgeons whenever he wishes, simply by using the three constituent parts on this book.