The “Race Against Time” scenario.

I recommend immediately leveling up Dugall's Diplomacy and Guardian Angel skills (if you can, you can also get a ballista). In this mission, there are 2 hidden archer outposts; I advise you to capture both and, over approximately four weeks, accumulate archers. Diplomacy can be very helpful; there are many small Haven units scattered on the map. After this time, you should have around 150 of them. Then, go and eliminate the garrison, first taking all the archers and other troops from the castle for all the money – there will be losses, but I advise you to lose as few archers as possible, and then attack the castle. This is where the Guardian Angel will come in handy. At all costs, protect the archers so that they are not blocked.