Proceeding slowly and vigilantly, you soon find your caution unnecessary. Apparently, this "Master" decide that discretion was the better part of valor and fled the dungeons beneath the moathouse. Of course, the fact that you slew or routes the majority of his forces may have something to do with his withdrawal.
Reaching the bandit's headquarters, you find a series of four linked, but now empty chambers. Everything that was once here is now gone. Deren spends some time looking at the floor, and can tell that the remaining bandits apparently took some horses and a cart, loaded them up, and left via a passageway that leads back up to the surface several hundred feet away from the moathouse proper. They have at least a six hour headstart on your group, and seem to have headed in a northeasterly direction.
The only thing of interest you find in the area is a tattered peice of parchment left on the floor. A hastily scribed note in the common tongue reads:
"Heroes of Hommlet:
You have made an enemy this day, the likes of which you have never seen. I shall be patient, and rain misery and torments upon your very souls before I release you, slowly, to the black despair of death. We shall see each other, very soon...
Lareth, Master of the Moathouse"