You've been underdeveloped for a while, but you finally decided to see the doctor about it, and he suggested a new, experimental treatment. You're nervous, but step-mom says its worth it, so you pop the dose and wait. You ask her to stay with you, not sure what the results will be, and before long...you start to grow. And grow. And grow. It's THROBBING, you can't keep it under the blankets for much longer! You ask her to help you, to look at it and tell you if its ok. When she pulls back the blanket, your cock springs up, ENORMOUS. HUGE. It's monstrous!! And she can't keep her eyes off of it. She seems to...like it. To want it. She looks like she can't help herself! And you're never going to stop her. God, no. She looks so good, stroking your monster dick, all you want is more. And that's all she wants, too!