He always thought his adult stepsister was plain and completely sexless, but secret observation reveals erotic lingerie hidden beneath her frumpy house clothes. Her true nature is shockingly aggressive: whenever desire builds, she goes out hunting for a man to fuck. On the one day she cannot find a partner, her frustration explodes and she attacks him instead. The stepsister he never truly knew rides and fucks him until she is completely satisfied, proving that he badly underestimated just how filthy she could be.