Caught By sis

I was 15 and very obsessed with the idea of sex, even though I was still very much a virgin. My love of sex even had me going through a phase of sniffing my own sisters dirty knickers while I masterbated.
My sister Sophie, s*******n years old and very pretty, all my mates fancied her, still living at home with me.
This particular day, It was the school holidays, I was at home alone, Muma and Dad were at work and Sophie has gone to town. I had layed in and had started to feel horny and had got out a porn mag and started to wank myself. But I needed a little something to help me along. I got up and walked naked into my sisters room and look around the floor, my sister was not very tidy and I would usually find a pair or two of her worn panties.
As usual I found a pair of briefs, I checked the gusset it was stained, I sniffed at it, taking in the scent of Sophie's pussy and couldn't resist having a taste of the gusset, my cock was rock hard and I was wanking like crazy, sat on Sophie's bed and looking through the dirty mag imagining I was sniffing at the girls pussies.
Next thing I knew, I heard my sisters voice, I looked around and she was stood in the doorway with a shocked look on her face.
I quickly held the magazine over my hard-on, then realized I still had Sophie's knickers up to my face.
She called me all the names under the sun and threated to tell Mum and Dad about me. I pleaded with her and told her I would do anything.
She went quiet the smiled 'Ok' she said.
She told me to show her my dick, I dropped the magazine and held it in front of her, she ordered me to pull my foreskin right back and exposed my swollen glands to her, I has pre-cum oozing out of it's eye.
She brought her hand forward and cupped my balls, it took my breath away, as it was the first time a female hand had touched me there.
She told me keep wanking, which I did, the then started to tease me, she picked up her dirty panties and held them to my nose and started to talk dirty to me, telly how I like to sniff my own sisters cunt!
She then got me to lay on the bed, she then did something that really suprised me, she asked if i wanted to sniff the knickers she was wearing? Wow this blew my mind, the very thought of them still being warm, but no! this was not what she meant! she got on the bed and lifted her skirt and straddled my head. I was gonna sniff her panties while she was still wearing them.
My eyes almost popped out as I looked up, I could even make out the line of where her slit was. She lowered herself onto me and my nose made contact with her crotch, only a thin layer of cotton from Sophie's vagina, this was it for me, as I started to shoot my spunk all over the place, all up my belly and hitting Sophie on her back and bottom.
This was not going to be a one-off as Sophie had the perfect blackmail on me and she was gonna have fun with it.