Brazie’s Black Book of Secrets

https://www.wowhead.com/item=49926 is a consumable item which "Contains some of the best kept secrets in Azeroth. Not for the faint of heart!".
It costs a whopping 22,000 gold and contains 5 books:

The NPC who sells these items is https://www.wowhead.com/npc=37904 and he spawns in Deathbringer’s Rise after the roleplay, after you defeat https://www.wowhead.com/?npc=37813 in https://www.wowhead.com/?zone=4812 as an Alliance player.

And yes, he’s level 69. Quite a gnome.