Travel to the Burning Steppes and find Grark Lorkrub. You recall Lexlort mentioning that he was last seen in a massive Blackrock fortress. When you find Grark Lorkrub, use the Thorium Shackles to bind him and then lead him back through Blackrock Mountain to the Searing Gorge. Lexlort will have his men waiting on the other side to take Grark into custody.
I tracked him across the Searing Gorge, through the mountain, and into the Burning Steppes. That traitor was caught red-handed giving the Blackrock orcs vital information about our day to day operations. I'm speaking of Grark Lorkrub.
He now sits in the Burning Steppes, safely under their protection - or so he thinks.
Take these shackles, [player]. Find Grark, place the shackles on him and lead him through Blackrock Mountain. Do this and a tribute is yours.