This is one of two quests that are running simultaneously ("The Bloodworm Helm" is the other). Both are straightforward object-retrieval quests, but you must retrieve both objects before you can complete the quest - no partial credit will be given.
The Council of Mages has split over how to deal with Mannimarco. The issue is not whether to fight back, but how to fight back. Irlav Jarol and his faction have stolen the Bloodworm Helm and gone to Fort Teleman, southeast near the border with Black Marsh. The Bloodworm Helm fortifies your Conjuration skill 2 points per 5 levels to a maximum of 12 points.
The Conjuration connection should be pretty obvious when you hit the second level. You are going to be fighting Necromancers on the first level and Daedra on the second. You'll find Jarol (dead) in the big chamber on the second level. It's unclear how he died. Perhaps he was attacked by the Necromancers and summoned the Daedra to fight them, but the Necromancers actually managed to kill him. Perhaps he was just killed by his own conjurations. In any event, get the Helm off of his body and deliver it to Traven after you have recovered the Necromancer's Amulet.
Traven is stunned to hear of Jarol's death and promises to keep the Helm and Amulet secure in the tower. Talk to Polus for your promotion to Master Wizard.