Congratulations on your promotion, Evoker. Strive ever forward and all that rot. What with the fallout from the Necromancer attack at the Wellspring Cave, personnel are stretched a bit thin at the moment. There is a minor matter, though, to which you are well suited and since you're otherwise unoccupied (translation: expendable), would you mind taking care of it? Go see Janus Hassildor, Count Skingrad, about a book that he borrowed that we would like to have returned.
You'll find Hassildor at Castle Skingrad, but you'll need to go through proper chanels, so speak to the steward, Mercatur Hosidus. He doesn't see why the Count should bother with someone like you, but he'll relay the request for an audience. Check back tomorrow.
Tomorrow does not really mean tomorrow. Although the wording gives you a sense of urgency, you can run off and take care of other business for a while because nothing is going to happen until you speak to Mercatur again. There are all sorts of caves, mines, ruins, Oblivion Gates, abandoned forts and the like to occupy your attention. So feel free to either indulge or simply wait a day. In simpler terms, you have to wait 24 hours or more before he will talk to you again.
When you come back to talk to Mercatur, he tells you that the Count wants to meet you outside of town near Cursed Mine (which he marks on your map) at 2:00 a.m. You don't need to mess with the mine, which is southeast of town, but simply meet the Count there at the designated time. Odd, but when is dealing with nobility anything but? Just follow your compass marker to the designated spot and wait. Or not. I prefer not. Rather than waiting at the exact spot, there's a good observation point behind some rocks above the meeting place. So stealth yourself and wait. Mercatur and two friends in Necromancers Robes will arrive at the designated time, but no Count. Most suspicious.
You're going to have to fight these guys in order to get the ball rolling. I prefer a good backstab at 6x damage, but then I like to sneak. Even if your stealth is next-to-nonexistent, you should be able to get off at least one good bowshot for double damage. Since you're above them, they're going to have to charge uphill to get to you, which will slow them down a bit and allow you to get off a couple of spells or arrows. If it gets to be too much for you, head for the designated spot and Hassildor should come charging out of the bushes and take them out for you.
He'll rag on you for being a complete fool (or the next best thing). And what made you think that you were being sent to retrive an overdue library book? The Count suspected that Hosidus was involved with the Necromancers, but had been unable to identify his friends, so your little episode did work out for the best. He suggests a bit more honesty in future dealings, but believes that you were simply duped by the Guild (which you were). Go back and tell the Guild that he is not involved with the Necromancers. While he has no great love for the Guild, neither does he wish it any great harm.
So back to Polus you go. He is appropriately contrite about the whole business, apologises for placing you in harm's way and is reassured that Hassildor remains aloof from the Necromancers. There's another promotion in it for you and he suggests that you go clean yourself up and check back with him when you're ready for another mission.