You can find info if you take the time to scroll, but I'll quote RabidPimpSlap for you.
"Go to New Ark City, go to the slums, force past the guy demanding a fee to pass or however you choose to not pay, go to sleep, return to the slums, you will be confronted and taken to the Don's Lair, talk to the Don, offer to do leg work (grunt work?), he'll tell you to find Cassie (used to be his slave apparently), go back to Cassie and talk to her about the Don, go back to the Don and Cassie will be there (turned herself in), talk to Fawn (sleep in your new condo and she'll knock at the door), progress with Fawn until you can visit her for sub/dom sessions at the Torture Rack, talk with her about the Don, talk to Sammy (bathhouse), LinLin (massage joint), Arlene (police station), find hobo in slums, give him least amount of money, find him at the strip club (he spent the money there, my last play through did not have current updates and hobo was not in the strip club or anywhere after I paid him, I found this out by research), talk to other hobo, once chaos ensues go to the Don's Lair (I've only played LD+ on free sites so not all updates are present there! if you do not have a safe place for Cassie, the game ends once you save her! This is as far as I've been able to go with Cassie's quest, so I'm unsure if anymore content has been made for her, but I imagine if you have a safe place for her, the game might not end? and I can imagine that you'll gain her trust shortly thereafter if not immediately! Hopefully others may be able to assist you further!)"