My older sister Jess and I were like chalk and cheese. She was the sporty, athletic type with the firm figure of a young woman. I was just a slim built, plain-jane type. She was into athletics, music and boys whilst I preferred my studies and hanging with my after-school activities group. We more or less led separate lives, got on well when we had to, but essentially gave each other space to do our own thing. Jess had a boyfriend Phil who was a couple of years older than her. He would meet her after school and drop her home sometimes. He, too, was the sporty type, but just another older boy as far as I was concerned.
That all changed one day when one of my after-school clubs was cancelled and I went straight home. Phil's car was parked just along from our house and I thought he and Jess must be home. I walked in and found nobody so I went upstairs to change. It was only when I reached the top of the stairs I could hear them. They were both panting and muttering inside Jess' room. I crept along the bedroom hallway until I reached her doorway. The door was slightly ajar and I peeked through the gap. I was shocked to see both of them naked with Jess sat astride Phil. She was slowly rising and falling and it was obvious what they were up to. They both seemed oblivious to my presence being wrapped up in their own pleasures. I could hear them whispering to each other about how good it felt in between panting and moaning.
I watched a little longer and felt a kind of tingling inside my panties. It was like the blood was rushing into my pussy and my heart began to race. I slipped a hand under my skirt and felt a dampness in the cotton of my underwear. I'd never had any experience like this before, it wasn't the sort of thing I'd discussed with my friends. I smoothed a finger across my panties and felt an extra special feeling as I passed it over my clit. I had done sex-ed at school so I knew where everything was, as such. Jess and Phil's motions became more vigorous as did my fingers probing across my tingling, panty-clad pussy. I crept away into my own room next door and shut myself in.
I could hear their exertions quite clearly through the wall now as flesh slapped against flesh. They were both moaning loader now and I knew they were in the midst of some session. I pulled my panties down and skirt up as I lay on my bed. I dragged a finger up my moist pussy and circled my clit. The feelings were awesome and continued rubbing up and down as I pictured them humping away just a few feet from me. I dared to push a finger inside me and wondered how wet I had become. With a finger half inside me I rubbed around my clit with my thumb. Jess and Phil were obviously nearing orgasm as I heard Phil say he was gonna cum. I now rubbed my soaked finger around my clit and the feeling I needed to pee grew stronger. I knew I wouldn't pee, it was an orgasm building. My first big 'O' was on it's way just as Phil and Jess announced their own. I supressed a little cry out loud as I clamped my knees together and pressed down on my clit. My whole groin area and top of my thighs throbbed as my orgasm hit me. My heart raced and my head felt light as I turned on my side, my whole body feeling in ecstacy.
I lay there for a minute or two before turning onto my back. My pussy was soaked, as were my fingers. I quietly cleaned myself up taking care not to let Jess and Phil know I was home. A few minutes later they left her bedroom and I checked out of the window as they both left in Phil's car. I'd had my first orgasm and it was the start of many more.