This quest is acquired from Dunwich, an associate of Havard-Pierre d’Amortisan, who can be found beside the westernmost location for the placing of the herb ward. Once you’ve placed the herb, speak with him to learn of the details. He will ask you to find evidence of a mythical beast, the Nox Morta. This can be found to the east, on the banks of the river near the Shattered Wall.
Once you have the evidence, bring it to Havard-Pierre d’Amortisan for inspection. From here, he will ask you to bait the beast to confirm its existence. Place the bait in Swamp Kuldsdotten and wait for it to appear. You will find that it is a large Bogfisher. Although it has a lot of health, it doesn’t deal much damage and can easily be taken down. After you’ve killed it, return to Havard-Pierre d’Amortisan to complete the quest.