The tablet tells much. But not enough! Not nearly enough! There is a book, a digest that Yagyin wrote in ages past. The... people I fled from... they keep this book in many places. And their most learned study it. It holds vast knowledge. Knowledge to protect us! Go to Keeper Bel'dugur in the Undercity of Lordaeron. Show him this sigil and he'll think you one of them. Ask him for Yagin's Digest...and bring it to me!