I got you. You have to talk to these character, Fawn (condo), Lin-lin (happy massage), Arlene (police station), Sammy (bathhouse), and the homless people near don's lair. These will help you but first talk to alrene and then homeless people cause to save her without losing you have to have arlene beat him.
When you first meet her she will say something like she wants to beat the guy. You will first ask for her help, she will say as long as the slums are quiet, the cops cant do anything, so go to homless people by dons lair and their will be one who will help. Well next day he will be gone and at the gentlemen club and then go back to where you met him and one will actually do it. Go back to arlene and that should get her to help. Sorry if any part of that is confusing, tell me if you need help on certain things.
so the people i said to talk to will make everything easier, fawn and sammy will give you the schedules for when there is the least amount of people, lin lin will help you take out the gaurds in the front. Fawn will also give you a key, cause when you have the homless people harass him, he will hide cassie in the basement, and thats what the key is for. The people will disturb him into putting her in the basement and that will seperate her from don, and arlene will help later when you bring cassie to saftey