Enter Longshadow Alley: Daeneth Cloister to find the liason between the vampires and the Thexians. He's on the dock at the far end of the Alley ( -47, 5, -63 ) Copy/waypoint -47, 5, -63.
She sends you to find the vampire hideout, and destroy the leaders of their operation. The hideout is near the Beggar's Court entrance ( -117, -53, -344 ) Copy/waypoint -117, -53, -344. Look for a wooden door in the stone wall to enter The Hidden Crypt.