"At last, Guardian. I don't know why you couldn't have come sooner. Perhaps all of this could have been avoided. When CluDathoon attacked, everything went to hell. Babette and Ezio were killed. When I saw the Resistance beginning to organize, I offered to use our Guild HQ as a Resistance HQ... but Nazir disagreed. As a result, he went his own way, and now threatens the Resistance. Last we heard, he's been hiding out in the ruins of the Southern Port of Avalon, on the other side of the mountains. Head South, over the mountain range, and kill Nazir near the docks."
Leave the Resistance HQ and head to Lower Avalon. Walk through the town and ascend the stairs that lead to Upper Avalon. When you reach the market, rather than go inside, enter the archway to the left of the market and walk to the stairs leading up the mountain. Travel up the stairs, then head down them on the other side to the Southern Port. Nazir is located at the docks. He will attack you when he sees you. Once you have killed him, return to Resistance HQ. Speak with Vlad for the next quest.