Brazie’s Black Book of Secrets 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 and he spawns in Deathbringer’s Rise after the roleplay, after you defeat in as an Alliance player.

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