In the final installment of the Step-Sis Bully (Part I, Part II) trilogy, Penny is not happy that Sam is late for their workout. Sam is even less happy when he finally shows up and she tells him his punishment for tardiness is panty discipline! Sam absolutely refuses but Penny knows doing the day's workout in nothing but a pair of her panties will go a long way towards whipping him into shape. Plus, it is always fun to give Sam a humiliating reminder that she is strong and he is weak! Penny puts a stop to his arguing with a headlock and begins ripping off his clothes. Sam fights back as hard as he can to avoid being put into panties by his hot step-sister but he is no match for her. Penny tires him out with bodyscissors and even when he wiggles out of her holds, she just easily overpowers him again and again. After dominating him on the mat for while she strips him naked and of course, the twerp has a little stiffy. After the beatdown Penny just gave him, his dick is the only part of his body that isn't limp! In the end, Penny has her way with Sam... in more ways than one!