Save the rest of the villagers

Sydiri Haunlar, one of the guards remaining in Nightstone implores the party to go save the villagers who have fled from the attacking giants.

The interrogated goblins mentioned that they fled to the Dripping Caves, about a mile north of town.

I don't recall a clear reward being offered, but the town's treasury was mentioned to be held by the Sword Coast Trader's Bank

The party entered the caves and made a deal with Hark to release the villagers if the party could remove a "black thing" from the water supply.

The party ended up encountering and defeating a Black Pudding near the water supply.

They report to Hark and urge him to release the townsfolk. He points to the cave, and Raloric reminds him that he promised some additional treasure. He hands Drork a ring with wings and a feather inlaid in it (that was on his toe) and a scroll (that was in the Ogre's loincloth), Stats in cat form identifies the items as a Ring of Feather-falling, and a Scroll of Gaseous form.