This quest is not available in game.
Return to Captain Garran Vimes in Theramore.
Well, judging from Captain Vimes's report, you've been a huge help to his investigation, and for that I thank you.
I can put my mind more at ease knowing that the matter is in such capable hands. If you would, I would request that you return to Captain Vimes and help him in getting to the bottom of this mystery.