Holy Fire in Rambleshire

The quest requires you to kill the Nightshade Abductor (x6) and find the Nightshade Letter (x1).

Guide on how to do it:

To complete this quest, head to the quest area and be sure to stand on the ground (if the character is in the air, you won't be able to detect the NPC). The Nightshade Abductor are invisible to players in their normal state, as they are in stealth mode. To find them, slowly move around the quest area and watch for debuffs. As soon as a debuff called “Unnerved” appears, it means that the enemy needed to complete the quest is hiding somewhere nearby.

When the debuff appears, immediately use the “Flashfire Thurible” item (provided upon taking the quest) near your character. This will allow you to detect the enemy you need to kill. Nightshade Letter will drop as part of the loot from killed NPCs, so keep hunting until you get it.