Mona and Steve were happy but something was missing. The only thing Mona could come up with was that she wasn't exactly what her husband wanted. He had a fetish for large breasts. She'd noticed how he looked at women in movies, at busty women as they walked down the street. Mona was beautiful, but she'd never be what Steve wanted.
Her only answer comes in the form of her friend, Liza. She was a beautiful, busty redhead with a kinky streak. She was also trustworthy. If Steve could get his fetishes satisfied by someone Mona felt safe around, then maybe he wouldn't stray permanently in the future.
Liza agrees to sleep with Steve, but it doesn't stop there. Mona starts to watch their encounters and Liza reveals that she's actually a professional dominatrix. She offers to take control over Liza and Steve's sex lives, training him to dominate her and her to submit to him. Mona becomes their sexual property, serving their needs, attending to them, and always putting their satisfaction above her own.
Mona never imagined that this is what her marriage would become, but she's happier as a sex slave to her husband and his other lovers then she ever was as just his wife. This is what happiness actually is.