Carmen's been having insane fantasies ever since her stepbrother, Damon moved in. However, unable to act upon her desires, she takes to the internet and writes down her most deviant thoughts in a blog called TheDirtyStepsister.com. The blog becomes Carmen's online diary which she assumes is only for her eyes, until she starts receiving emails from other stepsisters that share similar fantasies and before long - they're encouraging Carmen to pursue what she wants most - her stepbrother.