There are 2 abandoned houses on the beggar's nest map. Check each one. Failing that he's the guy in the abandoned warehouse. If you've done the beggar's nest completely you will not be able to get in there unfortunately. You went through the cult house I take it? (you have to use the wardstone to get through the door)
If so then bugger it. The quest will dissapear from your log after chapter one anyway. (unless you're a perfectionist like me and have to do every quest)
I do like to clear every quest i can,but on this one i think i mucked it up by clearing out the boss in this level before having a thorough look around, cos he was not in the wharehouse by the time i got there. <img src="/ubbthreads/images/graemlins/ouch.gif" alt="" />
Drink Up Ye Cider. 
