You returned to Toxer to find the town noticeably more nervous. A sing in the town square advertises the need for adventurers. Apparently, the goblin attacks on river traffic have increased and become noticeably more sophisticated. The city council promises you 1500gp if you eliminate the threat. You agree.
That same night you met Leatschleur Lumaine at an inn and he told you that he believes the goblins are encamped in the Underdark in one of the old duergar cities. The duergar cities hold a legendary (amongst bards, anyway) drum that he wants, and believes he can find. He will accompany you to defeat the bards, take a 1/5 share of the 1500 gp from the city council, the drum, and no other treasure.
You travel two days east upriver and find a burned-out river vessel. You track goblin raiders for one day going north, and fight and kill a small sortie of goblins guarding a hole. One escapes down the hole and you discover the hole is an entrance to the Underdark.