A 19-year-old girl isn't satisfied with just fucking her classmates, so she manages to get into a sex party, but what she doesn't expect is to find her stepbrother there, where she'll do all her perversions with him without even knowing who he is. When they reach climax, they take off their masks and find out what they just did. The next day, they struggle to look each other in the eyes at home. The stepsister is hysterical whenever they're around, but it's because she has a hard time containing her desires for her stepbrother. Desires she won't be able to contain, and they end up falling into sin.
