Lilith Ripinski is a 15-year-old loner, with an annoying 17-year-old brother named Samuel. One day, he pushes her just a little bit too far, and they enter into an intense, surreptitious sexual relationship. "The Book of Lilith" chronicles the development of their incestuous dynamic, their struggle to keep it secret, and the way Lilith's confidence grows as a result of feeling desired for the first time.
A beautiful mother walks in on her son while he is in the shower and becomes his lover. Together, they begin a voyage of lust in which they explore and fulfill all of their sexual fantasies.