Lost Soul
Head to this quest marker close to your starting location to begin this quest.
Here you will find Liam. He stops you from going down that path since it is "nothing but horrors"
He asks your help so that he may live. The difference of letting him live or die is that if you let him live, he will come aid you later on. If you let him die, he will return as a vengeful spirit. So its best that you help him.
Head to this location to find the Spiky Muskweed he needs.
It will be guarded by some enemies so take them out before getting the Spiky Muskweed.
Give it to Liam to heal him and he will get out of the way allowing you to cross.
Next, continue on the path to search for the person who hired Liam and his mercenaries, Gloria.
You will come across another NPC named Albert that asks you to save Gloria ahead. You find Gloria though and she accepts her demise.
If you didn't save Liam, the Soul Collector summons Liam's soul to fight you.
If you did save Liam (like this guide suggested) he will come rushing to your air before the fight starts.
Defeat the Soul Collector and receive some neat loot and the "Soul Collector Phylactery".
The last choice of this side-quest is a choice of saving Albert using the Soul Collector Phylactery or letting him die so you can keep it. Saving him nets you more exp while keeping the Soul Collector Phylactery only allows you to sell it for 3000 gold later on. The choice is up to you. (I used it to save Albert)