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This quest begins automatically when you speak with Dethmold during the quest Conspiracy Theory. You’ll find out that you need 4 artifacts to lift the curse and the mist. One of the artifacts is a particular piece of armor that holds the essence of courage.
To find the armor you’ll need to progress through most of the Conspiracy Theory quest up until the point you find and deal with Vinson Traut. Once he’s been killed loot his body for Seltkirk’s Armor. Once you have this armor this quest is completed and you can continue your search for the other artifacts.