Neville Brightwhistle is a NPC located on the north side of the Underworld. Once you complete his quest he will give you a Talisman of Goblin Slaying. To recieve your reward you must escort him to Dugan, located in the npc camp towards the begining of the Underworld.
Neville will follow you by either walking all the way back, or by using the teleporter system in the underworld. The sparkler to the northwest of Neville's location will take you to the sparklers to the east in the Underworld. Re-entering those sparklers will take you to north set of sparklers in the Blood Elemental room, follow the hall south to the exiting sparklers, which take you to the Undead room towards the begining of Underworld. Exit the room to the southeast and follow hall down to Dugan. Sounds complicated but it is faster/safer than walking all the way back through the Underworld.
NOTE: Currently there is a bug with this new S.A. quest that requires you to exit through the doors that Dugan is located and re-enter for the quest to finish. You may need to exit/re-enter a couple times for the quest to recognize the finishing point.