How do I join the thieves underground?

Well thanks for the answer re: Mr Black, now please tell me how to join the thieves underground.
I killed Witless at the bridge in Shrouded Hills and the mayor in Tarant will not give me any info.
The little guy in the park in Tarant will not help me either all he does in insult me And the guy near the flop house does not give me any info.
Thank You

 

Go back to the entrance of Tarant. Right by the bridge, there should be a lady in a purple dress. Talk to her and do her quest. Once that is done, go talk to the man at the bar in Madam Lil's. He'll clue you in to the Underground, and from there, you should be set.