Drops from the shadowman mobs holding books (or, in-universe, they are animated books that write in themselves). Names are "a treatise on vampirism", "a reference of discord", "a book of spells", "a compendium of lore" in the library of Demiplane of Blood. This is where Ariahn Teller, the NPC you turn the sister's handkerchief into to negate the zone-wide AoE + snare, stands in open-world Dreadspire Keep, but they only spawn in the DPoB instance. This is also where the bookshelf is clicked to head up towards Mayong.
Edited, Jul 13th 2022 9:25pm by Andhrimnir