Gwen wakes up before you

You wake up groggily to the sound of groaning. You open your eyes and lift your head to see your sister, still in bed, with her hand wrapped around her hard cock, stroking it up and down like she did for you yesterday. You feel a wetness between your legs, as though out of empathy. Her dick looks far too good to pass up.

You wait until her eyes are tightly closed. As quietly as you can, you crawl from your makeshift bed to the side of hers. You stand up, and quickly -- before she can notice you're there -- you climb onto the bed, straddling her with the bottom ridge of her manhood nestled wetly between your folds.

Gwen's hand lets go of her meat and her eyes fly open in shock. "John!" she shook her head, correcting herself, "Sarah! What the hell do you think you're doing?" she whispers harshly.

"What's wrong? It's not like you're inside of me." You smile wryly. "Besides," you continue while sliding your cunt up and down the bottom of her shaft, "doesn't this feel good?"

"Yes-" she almost says. "No! We can't do this; it's too close to something far more dangerous!"

You don't slow your motion, though. You slide your nether lips all the way up and down the pole wedged between them. Both you and your sister watch the glistening glans appear and disappear under you as you move. You pause on the tip, grinding your hips enticingly. This elicits a groan from Gwen.

"Agh! Seriously, you have to stop! Get off me!"