The Nithing - Skellige
Quest Giver: Rannvaig Notice Board or Lothar
Other Requirements: N/A
You can begin this quest one of two different ways, the first and most common way is by picking up the notice from the Rannvaig Notice Board. Alternatively you could also speak with Lothar who is nearby the town of Rannvaig.
Note: In the same area as this quest you'll also find the Armed Assault Quest which is easy enough for you to do while here.
For the first part of this quest you'll need to travel southeast of Rannvaig and speak with Lothar who is by a lone hut. He'll tell you of a curse that has been placed upon his son and he asks for your help. Inspect the area with the curse by Lothar's house and follow the foot prints which will lead you to a female Skelliger's shawl - inspect it to acquire a scent.
Now you will have to follow the scent back to Rannvaig where you'll lose track of it. Ask the unnamed Skelliger Women around the village until one of the ladies by the water tells you that the shawl belongs to Jonna, the town's herbalist. Speak to her to advance the quest forward and also to force you to make a choice.
There are two different paths you can take in this quest - you can reverse the curse onto Jonna and cause her to die/leave town (it doesn't really say what happens to her - she disappears from the game shortly after completing this quest though). Or you can have Lothar return to Rannvaig to live with Jonna, unhappily ever after.
I strongly recommend you reverse the curse on Jonna, just make sure you browse her inventory and buy any of the recipes or items she sells before you do so. Choosing to force Lothar to live with this psycho lady would arguably be the evil ending, since everyone's live is destroyed - except maybe Jonnas.