I have always been attracted to my wife's sister. She is very cute, younger and has a nice body. She would often wear tight shirts and shorts, exposing her young curves. Every now and then, she would give me some nice crotch shots, which provided me with some great masturbation material for the spank bank. She is a bit naive and would do this unknowingly, having no clue that her brother-in-law would be at all interested in her.
One summer, she came to visit us in New England for a week. It was a hot summer morning, and I was very horny. I was trying to sneak in a quick jack when my wife came into the bedroom after taking a shower. She thought I was asleep, so I had to stay still, which killed the moment. Finally, she and her sister left to go shopping for the day. I was grateful to finally have some alone time to myself. I went into the living room and got comfortable with some material. As I am stroking away, I notice my sister-in-law's suitcase in the corner. My cock was ready to blow, but something told me to wait. I was so nervous; my heart was literally racing with my thoughts of finding her panties. If she ever found out, I would be in such trouble.
I opened her suitcase and looked under a shirt. True to her personality, all of her panties were folded perfectly and in order. I thought for sure this was her own security system. She would know if someone touched her panties because they would be out of place, unfolded, etc. I finally got the courage to pick up a pair, white, soft...perfect. Paranoid, I practiced folding them to remember how she did it. Finally, with my throbbing dick twitching for some attention, I opened up her panties and placed my cock on top of them, right on the pussy panel. The sensation of her panties against my cock combined with my heart beating faster and harder, made the experience unforgettable. It only took about ten strokes, and I shot a huge load onto the floor. I made sure the cum did not make a mess on her panties. However, I decided to wipe the last drops of cum off with her panties. I figured her panties deserved a taste for giving me such pleasure. It was a great masturbation moment, and when the time is right, I hope to do it again.