Outside world as in beyond the mistwall where the humans are, right?
Anyway, here's how I see the plot so far all things included. I don't have the CDs, so bear with me.
This wizard that Bengaley spoke of, to me, could be evil! It's just not a real quest without an evil wizard, neh?
Anyway, this evil wizard wants this artifact because it is the key to a weapon he has been creating. The exact details of this weapon are unknown to me right now, especially since I don't really know the limits of lux. The dagger that Aven has is a failsafe, another artifact that can deactivate and, after all this time, could destroy the new variation of the weapon the wizard is secretly building, like in the swamp or something under a ruin of the original weapon's creators' towns. Or maybe it's even right under the nose of the elders in Sanctuary! Who knows?
So, the (very vague) nature of the ancient mystical dagger is revealed in the letter that Aven has, which instructs him to find out all he can about this little doo-hickey with help from his companions (and one or two experts that can help out). The original nature of the key, the dagger, and the weapon have been lost to time, and only exist in well preserved but mainly forgotten logs in scattered libraries. The records are nebulous about the things themselves, as they are only ballads and fragments of biased contemporary writings.
So, Aven reads the letter, and gets contacted by the wizard. The mercenary could have been already contracted by the wizard. Everyone involved goes to see the one that the letter directs them to, right there in Sanctuary. And then, well, we'll see. How's that? Subject to drastic change and all that, of course.
"Every revolutionary idea seems to evoke three stages of reaction. They may be summed up by the phrases: (1) It's completely impossible. (2) It's possible, but it's not worth doing. (3) I said it was a good idea all along."
-Arthur C. Clarke