Take the Singed Letter to Thorius in Ironforge. He is in the Hall of Explorers.
If you are reading this letter, I am no more. How it got to you, I do not know, but thank and reward the ones responsible.
About the stones: They exist and the Dark Irons have them in their possession. Their leader, Lathoric the Black, is using the power of the stones to enslave my excavation team. They were taken to the cauldron. Their minds are twisted, working night and day to complete something called Obsidion.
Help them, brother. It is the final wish of a dead man.