Note: This story was dynamically reformatted for online reading convenience. It was a sunny lazy afternoon as Mike settled down in the sun lounger, he closed his eyes and started to drift off into a light sleep. A while later he opened his eyes slightly to watch the form of his younger sister by 2 years come out of the house and walk towards him. She was wearing a one piece swimming costume and he could not help appraise the shape of her body, maybe a couple of pounds overweight but pleasantly ripe looking. She had a small pair of breasts that moved only slightly as she walked, and he could see the indentation of where her belly button was. His eyes drifted down to the slight bulge of her pubic area framed by pale thighs. She must have been aware of his gaze, as she looked at him and for an awkward second or 2 caught his eye, causing him to quickly look at something behind her to pretend that he hadn't really been ogling her young body. He knew he really really shouldn't be looking at his sister like this, he knew it was wrong, but something had happened 3 days ago that he had not been able to stop thinking about ever since. He tried to not let the same thoughts loop endlessly, continuously making him horny, but he just didn't seem to be able to snap out of it. The only small excuse that allowed him to think like this was that Sarah was not his biological sister but had come along when his dad had married Sarah's mother. Still, Sarah was only 3 when this happened, so she really was to all intents and purposes his sister. He really wished he could stop thinking like this, but closed his eyes and started to replay the shocking and incredible memory once again. His sister Sarah had been going through an awkward stage, and his mother was starting to get desperate. It seemed to be the final straw when she found a packet of cigarettes in her pocket, and it seemed to Mike that his mother just flipped. He and his sister were in the lounge at the time, and his mother had stormed in shouting at Sarah, 'Just WHAT are these doing in your pocket young lady?'. Sarah came out with a load of excuses that wouldn't have fooled a child, and then the incredible and shocking thing had happened. 'Right, that IS IT!, come with me to your room NOW!'. She then grabbed Sarah's arm and hauled her off the sofa. Sarah was looking very worried as she cried 'What are you doing, get off!', his mother had then come out with the words that had immediately raised Mike's blood pressure and caused his cock to rise almost immediately. 'You are going to get a damn good spanking, now come with me!' He caught the look of horror on his step sister's face as his mother hauled her off to her room to be spanked. Mike was beside himself, his sister was clearly too old to be spanked, but it appeared this this was exactly what his mother was going to do! Quickly he rushed upstairs to his room, which was directly next door to his sisters. He put a glass to the wall and listened. He could hear everything! 'Please, Mom No! .. you can't possibly spank me, I'm not a child!' 'Pull your Jeans down NOW!' Next he heard the sound of sobbing and he assumed that his sister was indeed pulling her jeans down. This was all too much, and as he listened he dropped his own jeans and underpants and started to gently masturbate as he anticipated listening to the sound of his sister's bottom get spanked. What came next was the icing on the cake. 'And your knickers' came the voice of his mother. This sent even more of a shocked erotic charge through Mike 'MOM! .. NO!, you can't be serious!' 'I am perfectly serious, and if you don't do it NOW I will haul you downstairs and spank your bare bottom in front of your brother. The choice is yours' This was almost too much for Mike to take, but he held back. For the next few seconds all he could hear was her sobbing, and he guessed that unfortunately) she was not going to be spanked in from of him. 'Now bend over my Knee' More sobbing. Mike could see in his minds eye the sight of his sister, naked from the waste down, vagina clearly on display bending across his mothers knee. SPANK! 'OW!, mom please that hurts' SPANK! SPANK! 'then maybe you'll think twice about smoking!' SPANK! SPANK! SPANK! SPANK! Mike was ready to explode. He could hear the sounds of his mother's hand smacking his sisters bottom and could visualize her red plump cheeks bouncing with each stroke, and her legs parting slightly as she wriggled in pain exposing her pussy lips. He finally came just before his mother had finished the spanking, then collapsed on the bed exhausted with the whole sexual tension of just what had happened. So this was why Mike has started to look at his sister in such an inappropriate way. He had no idea how to stop what was starting to feel like an obsession, but things were going to get a whole lot more intense as events unfolded over the next few days.