Right from Silverglen you find Bjorn, Mara and his almost dead mount Alfie. Talk to Bjorn and discuss Alfie with him and tell him that you can help. Next talk to Alfie and say that you have a way to heal him (you need a Bloodstone in your Inventar. If you don’t have any Bloodstones, in the Infiltrating the Immaculates Quest you get two.) – Quest completed.
Now you need to escort them to Silverglen (The Escort Job), after you completed this Quest you get the Man on the Silver Mountain Achievements.