I can't believe I did this.
I had married a woman with two daughters from a previous marrige. The eldest one, Lisa, had started being real 'casual' around me when she was about 16. This eventually lead to some minor hanky panky a few years later.
She had left for college and was away for a few months before coming home for a weekend when this happened. Upon arriving home, her mother couldn't spend enough time with her. They talked well into the night. Eventually they headed for bed still talking. My wife asked me to sleep on the couch so they could continue into the night.
Several hours on the couch made me uncomfortable so I slipped into the bedroom to get a book. I thought they were both asleep but as I passed the bed Lisa gave my leg a little rub. I looked down and just from the hall light I could see a wicked grin on her face. Just then my wife who was laying in the same bed groaned and rolled over. Quickly I dropped to the floor so not to get caught. Lisa snickered and whispered you ain't doing anything wrong...yet.
Taking the hint, I noticed her bare leg sticking out from the covers. Slowly I worked my hand up her smooth skin until I found her boxer shorts. Her legs parted slightly as I slipped my hand up the leg of her shorts and found her sopping wet pussy. Laying on the floor a few feet from my wife, I played with my step daughters clit and fingered her pussy. She moved slightly and moaned very softly so as not to wake her mother as my fingers worked their magic on her wet pussy. Eventually she held her breath, her legs tensed and her pussy spasmed on my fingers. I raised up a bit, she smiled at me and I quickly left as my wife stirred once more. I was in the bathroom with one hand on my rock hard cock while sniffing the still wet fingers of the other hand shooting a massive load in seconds.