Book of Madness
The Book of Madness is the only existing tome detailing the horrors of the Old Ones, the Outsiders and the Outer Gates. The copy is currently held deep within the vaults of the Ars Medievalis. It is reputed to contain such horrors that it drives those who view it insane.
In 1936, Agostino Selletti viewed the book in an attempt to gain information on a Bound Abomination. He lost consciousness, which allowed a Spirit of Intellect to inhabit him in order to escape from the Library.
Agostino was unable to find the information he was seeking, and the book remains in the vault.