Stefan at Ebon Watch wants you to go to Voltarus and complete any tasks Drakuru has for you. While there, you are to steal 5 Harvested Blight Crystals. If you lose your Ensorcelled Choker, return to Stefan at Ebon Watch to get another.
1x Drakuru's task complete
Blight crystals?! What could this scumbag Drakuru be up to? Clearly, he's working on something significant.
Continue to do his bidding and perhaps once he's more familiar with you he'll reveal his plans. In the meantime, we need to have a look at these crystals.
While you're in Voltarus, try to get some samples of the harvested crystals when no one's looking.
Be alert! Handling those crystals can trigger your disguise to fail.