After completing The Penetration quest, return to your home and try to call the School on your landline phone.
No one picks up, so you decide to go to the School yourself. Knock on the Gate and eventually the Principal will come outside and tell you that the Field Trip you thought your sisters were on ended weeks ago and they should have been home.
Go to the Police Station and speak to Aaliyah at the reception desk. She tells you she'll handle the paperwork and that you should go investigate for any leads. You decide to search Ashley-Kate's Diary.
Go back to your house and look in Ashley-Kate's Drawer to find her Diary.
Go to your basement and ask Abbie to unlock the Diary.
You read the Diary and realize that Ashley-Kate and Mary found out about your large debt and went to find work to help you pay it off. They ended up getting hired as strippers at the Nightclub! Go there to find them.
When you get to the Nightclub, talk to the Bartender. He mentions Poppa and suggests that Ashley-Kate and Mary might be at another club, but he won't give you anymore information unless you spend some money, and so you are forced to choose one of the strippers for a private show.
Just keep clicking on the alcohol in the room to progress the scene. You'll get drunker and drunker. Eventually the Bartender will come back and tell you that the girl you chose had an accident and they're sending a different girl instead.
After you drink so much booze you have to sit down, a purple-haired girl enters the room and starts dancing for you. She begins to strip and you end up having sex with her. You hear her voice at one moment and realize it's your younger sister, Mary.
If you cum inside of her, Morality decreases by 5.
You try to talk to her but she seems brainwashed. You quickly throw on your clothes and carry her back to your home. You wake up in your room.
Go downstairs and talk to Mary. She doesn't seem to remember anything.
You realize you're not feeling well and pass out.
When you wake up, you look in the mirror and see that you've transformed into a girl!
You don't dwell on it long, however, and put on your clothes. Go downstairs and you will be taken immediately to the Nightclub.
Speak to the Bartender, and he'll mistake you for "the new girl" and bring you to the same room where you had sex with Mary so you can meet Poppa.
While you're waiting for Poppa to show up, you transform back into your male body.
Poppa shows up and is not pleased, and realizes who you are. He hits you so hard you collapse and then demands $10,000 if you ever want to see Ashley-Kate again.
You pick yourself up but keep the school girl outfit for later. You can walk freely out of the Nightclub.