I was past the point of thinking twice, so I worked my shorts down and also got my shirt off. I turned to my side again, facing her back in the darkness. She move back against me and encouraged me to wrap my arms around her, and I did so cautiously. I wrapped my arms around my sister's small waist and she put her hands on mine where they rested on her stomach. Being naked under the sheets, holding my sister, sent a tremor of nervous anticipation through me.

"Go ahead." she whispered.

I gently began to push my penis upwards, guiding it a few inches along her butt cheeks....