The Sewer King's Hideout

From the description:

The city of Fallmourne has been plagued by a group of bandits known only as the Grey Fingers. Their leader, a half-orc named Gorek Felhand, has used Fallmourne’s robust sewer system as a way to move his men unseen across the city. Recently however, a defector has come forward. Tired of mistreatment at the hands of the gang, he’s given the authorities the location of their hideout. The local authorities have offered a reward of 100 gp to anyone who can bring them Gorek’s head.