You are the thief hired to infiltrate into the former builders/now thieves fortress somewhere in the mountains and steal some blueprints of new weapons and at the same time you are to find out what's happened to your "colleague" here. And here begins your journey during stormy night.
While the scenario is relatively thin, this mission proposes quite a variety of locations: valleys, mountain caves, mines, and partly underground - partly upground fortress. Heck, you can even fly on balloon (one of legitimate exits into fortress which can sifnificantly alter your experience of your further path)! And sometimes there are less obvious ways into our objectives (and authors sometimes go with this even a bit too far - like with finding exit from valley where we start). The tasks are mostly reasonable and simple to perform (with one exception) - but some small switch hunt is required, beware. The mission is quite challenging, especially with lots of torches here and there, and encourages careful use of your resources.
The mission is updated to v5, which is amazing and shows that authors still do not give up with this, but some problems are present (I haven't played previous versions): the loot goal on expert really turns adventure into a slog and makes you searching even after other main tasks are accomplished; in addition, the mission sometimes is quite laggy which could be an issue in outdoor, open locations. Looks like, v6 is still possible. Aside these nitpicks, Siege Shop is fun and challenging mountain romp, which I recommend to play - on lower difficulties first.