After the death of Jarol and Caranya's betrayal, Traven has apparently decided to fight fire with fire, as it were. There is a very special Black Soul Gem in the possession of some Necromancers at Silorn, an Ayleid ruin near Skingrad (just go southeast from Bloodcrust Cavern). He has dispatched some Battlemages to the site to take it, but wants you to go take charge of the operation. He won't tell you anything about the soul gem other than it must not get to Mannimarco. So hit the road, Jack, and don't come back empty-handed.
When you get to Silorn, you'll find three Battlemages hiding outside the ruins. Their initial plan fell apart because the entrance door is enchanted and they lost one member of their party when they tried to assault the place. Now they're planning an ambush to seize the stone when the Necromancers try to take it out. But you're in charge, so they'll follow your orders. There are two patrolling Necromancers out front, so be cautious in how close to the entrance you get.
You can either go along with their planned ambush (which is somewhat helpful to you, but runs the risk of getting one or more of the Battlemages killed in the process), or you can try to take care of it yourself. Which way is easier depends on your combat skills. If your skills aren't that great, go along with the ambush plan and you can be the backup plan. If your skills are decent, either have them sit tight or set up their ambush a ways back from the ruins so that they can clean up anything that gets past you. Since I tend to play stealth-oriented characters, I generally go with the latter plan. I have run through this with one VERY combat-oriented character and managed to do it solo.
If you decide to go with the ambush plan, each of the Battlemages has a specialty and a recommendation on where they should be. They'll have a much better chance of survival if you follow their recommendations. Now the only question is whether you have them set up close to the ruins or farther back. If you set up close to the ruins, it's going to turn into a real slug-fest very quickly because these guys can't hide for nothin' and the Necromancers detect them very easily. So do what you can to support their ambush. When everything is ready, talk to Thalfin. Two other Necromancers will come out and join the two that are already out front. They'll be followed by Falcar (your old friend from Cheydinhal).
If you've set everything up right and can get behind the Necromancers without being detected (circle around the other side of the big statue), you can cut off Falcar's retreat into the ruins. A good Paralyze spell or poison can keep you from having to go dig him out of the depths of the ruins. Then you can just collect the soul gem and be done with it. If that doesn't work, you're going to have to do it the hard way.
Silorn has three levels inhabited by lots of undead and Necromancers. Falcar is at the bottom of the last level (isn't it always that way?). Everything is kind of scattered out and there is a decent amount of loot in the ruins, so the hard way will definitely be the most lucrative.
Report back to Traven and give him the gem. Since you're already a Master Wizard, there is no promotion or other goodie for you. If you're not careful with the mission-completion dialog, though, you'll launch right into the last mission.