My company recently had our morning Xmas party and that been my first I got pretty shit faced and needed to be driven home. As I got home I noticed there were no cars so I stumbled to my flat outside and crumbled into my bed fighting my dizzy head and my need to throw up! It was just after 7 in the evening when I woke up desparate for a piss and a raging hard on to tell me so. I forced myself up and decided to piss in the gaden to woozy to walk to far. As I felt the wonderful feeling of pressure been realeased on my bladder I looked up to my 13 yr old sisters room and noticed her and her friend standing naked looking at themselves in her mirror. Mmmm, pussy is pussy so I finished my piss and quietly made my way closer to her room. I had seen my sisters tiny pussy and tits before but her friends were new and my sister had grown! As I stared into her room I took my cock in hand and gently started to stroke. The girls were looking at each others pussys and my sisters friend bent down and gently put her finger in my sisters pussy and told her she had got wet from her story while bathing. My sister had closed her eyes while her friends finger was in her tight little snatch and she was now pulling on her little pink nipples and breathing that little harder. My cock was now at full attention and as I rubbed my thumb over my cock head I could feel my pre-cum leaking out my piss slit. My sisters friend was now rubbing her pussy even harder and when she pulled out a black marking pen and put it in my sisters pussy I nearly blew my load. I decided as horny and as turned on as I was I wanted to try and last a little longer so I looked away and undressed myself. I looked back just in time to see my sisters face contort from pleasure and pain as she came on her friends fingers and penwhile her friends face was sucking hard on her nipples! I took cock in hand and jerked myself harder than I had ever done before and I exploded with a force that stunned me. Cum flew every where including just short of my sisters window. As my stroking slowed to a blur I saw my sister lying on her friends chest pinching her beige nipple asking her to give her 5 minutes just to recover. I slowly gathered my clothes and walked slowly away, stopping to have 1 last look back at my sister and her friend who was now starting to open her legs and display that beautiful innocent teenage moist pussy with the black marker pen peeking out her tight little slit!