Speak to Tyrion in Stormwind Castle.
Hmm, an interesting tale, and not one to be taken lightly. Yeah, I can help you, but what you need to do is divvy out a form of justice that's not... legal, if you're to see this through to the end.
Lescovar and Marzon need to be dealt with, and swiftly. Do you think you're capable of such a thing?
You decide. If so, then make haste to the castle and find an old friend of mine, a gnome named Tyrion. He's been watching Lescovar now for a couple weeks. He should be able to help you end this.