Investigating the Starting Point

Well now, Adventurer. How about we do something like this. Search the hut in the woods first. Isn't it obvious that that place is the cause of all this? Rather than investigating the poisonous fog all over the place lets' search the most suspicious place first for clues. The soldiers say it isn't that dangerous, but you must be cautious since it is indeed unpleasant.

Let's search that suspicious hut first. Don't you think there will be clues there?

Yes! It seems like you've found out some information. What was created as a result of experiments, flowed into the lake. We're one step closer now that we know the cause. A solution must lie at the end of these clues, won't it?