According to Gothwan's information, Karzov is hiding in a safe house nearby, while the Crown is hidden in their headquarters. Before we can move against either, we need to reduce the number of potential reinforcements. A trek through the Tatters should provide ample opportunity for that.
When you've cleared the area, meet with Private Zoey Fargo. She's keeping watch over the safe house where Karzov is hiding.
Yes, I helped steal the Crown of Neverwinter! I was a loyal Nasher, but after Karzov left me to die down here, I don't owe him anything. I'll tell you what I know about where Karzov is now, and also where he's stashed the Crown.
Hey, if you see that treacherous bastard, remind him that loyalty works both ways - preferably while you're twisting a blade in his guts!
Glad you made it, <name>. You've been giving the Nashers a real thrashing. Wish I could've been out there helping, but someone had to keep an eye on the safe house. By the look of things they've figured out we're on to them.