Search around and find the Mysterious Box. It's locked, and you need to find some way to open it.
Use a Meditation Pill to sneak into Natalie's house. Peep on Natalie bathing to discover her unique tattoo on her foot. Use this knowledge to enter her basement, where you will meet Abbie, her sex slave. Regardless of what you do with Abbie, after leaving Natalie's house Abbie will appear in your Basement.