Liberation or Apprehension?
This is your first quest from Arch-Mage Traven. Except from midnight to 6, when he's sleeping, he'll be in the second-floor Council Chamber. Turns out that the Guild has had an informant, Mucianas Allias, within the Necromancers for some time. But no one has heard from him in a while. This raises questions on the validity of the information that he has been providing, so you're going to have to go talk to him and convince him to "come in from the cold," as it were. The Council dispatched a group of Battlemages to an Ayleid ruin called "Nenyond Twyll," but Traven worries that they'll probably kill him. So you need to get to him first.
Nenyond Twyll is northwest of Pothole Caverns. Alternatively, it's just about due south of the Waterfront District, near the border of the West Weald. You can't fast-travel there, so choose the closest location where you have been and go overland.
Once you arrive, you'll find that the Battlemages have beat you. And got royally spanked in the process, too. Fithragaer is the only survivor, but he's not about to give up now that help has arrived. He tells you to follow him and then charges down the stairs, right into a trap (one of those floor things you saw in Vahtacen). Why is it that NPCs think that a frontal assault is the best tactic under any circumstances (aside from being more easily scripted)? So now you're on your own.
This is pretty much a typical Ayleid Ruin, replete with traps, and populated by a bit less than a dozen Necromancers and various leveled undeads. So cautiously work your way down and through the ruins until you get to Mariette Rielle, the more-or-less boss of the lair. She has a god-awful detection range and I've never been able to take her out and avoid her evil villain rant. So just be prepared to deal with her and whatever it is that she manages to conjure up. She tells you that Allias has been turned into a Worm Thrall (a zombie, for all intents and purposes). You'll need to verify this, though. So search around in the big room at the bottom of the ruin until you find a button that opens the secret chamber where he is. Go ahead and put him out of his misery and you'll get a journal update telling you that you've accomplished your mission.
Go report to Traven and then go get your promotion to Warlock from Polus. The promotion gives you free access to the Council Chamber so that you're no longer tresspassing on that level.