Where can I find the aforementioned Aran? I went to the Shadow Thief Guild but he was nowhere to be found. Also how do I open the secret door in the guild?

C'mon, c'mon I'm gettin' itchy!!

remember that guy who came upto you and told you the shadow theives would help you (when ya entered the slums the first time) I forget his name, starts with a G or somethin like that, hes got a house in the slums I believe. If ya allied yourself with that back stabbing vampire wench ya can kill that guy and hes got a key which ya use to unlock the hidden door in the theives guild

oh and Aran is deeper in the theives guild (behind that door)