"Hello, Guardian. You know, it's situations like these where allegiances become most clear. When CluDathoon attacked, the Thieves' Guild was well protected from the effects of the Camlann Device, since our Guild is deep underground in the Sewers of Lower Avalon. When I suggested we join the Resistance to increase our chances of survival, not all the thieves agreed. In all of the chaos, Kcin was able to take control of the Thieves' Guild, and my former guild mates, Tribbs, Zamber, and Yorel now follow him. I can forgive my former brothers, but I can never forgive Kcin. He manipulated and lied to them in order to gain their trust. Go to the Thieves' Guild in the Sewers of Lower Avalon, and kill Kcin."
Exit the Resistance HQ and head to Lower Avalon. Use your compass to guide you to the sewer entrance that leads to the Thieves' Guild. Fall in the entrance and walk down the path. Follow the path with the Thieves' Guild banners hanging on the wall. When you find the hideout, walk behind the desk and step on the button on the floor. The button will open a secret passage in the wall next to the desk. (Hint: if you are a member of the archery class, you can use the teleport arrow to shoot into the passage when the doors open and teleport inside. Walk through the door and find Kcin in the back of the room. Kcin, Tribbs, Zamber, and Yorel will all attack you, but you only need to kill Kcin to complete the quest. When you have done so, return to Resistance HQ. Speak with Love for the next quest.