I was bored out of my skull, it was a Friday night and I should have been out enjoying myself, but everything had gone wrong that day, first the party one of my mates at school was giving was cancelled, then I discovered that most of the crowd I hung around with had been collared by their parents to do various things. So I was forced to stay home, across the room my twin brother was looking as bored as I was, not that he looked like me at all, we weren't identical twins just born within a minute of each other, me being the oldest by that minute. There we sat, two fifteen year old boys, and there sat our eighteen year old sister who had been assigned to baby sit by our parents who had gone off for a long (and I suspected dirty) weekend. Don't get me wrong, I love my sister and I think she's a dishy bird, but at fifteen I felt a bit miffed that my parents thought a baby sitter necessary.

"What's on the box Pete?" I asked my brother.

He picked up the telly guide, glanced through the listings and sighed.

"Bugger all." he replied.

"Andy," my sister said, "why don't you read a book or something."

"I don't feel like reading Becky." I replied.

"So what do you fancy?" she said sharply.

"Hell," I grinned, "I don't know, but sitting her doing bugger all is not my idea of fun."

"Put a video on." She suggested.

Peter got out of his chair and walked over to the video shelves, he winked at me and pulled a video off the top shelf, I grinned at him, as I knew that the top shelf was dad's collection of hard-core porn. From where she sat on the couch Rebecca couldn't see what our brother was up to, assuming he had picked one of the action video's she went back to her magazine. I watched Peter put the tape in the machine and turn on the telly, using the remote he set the telly to the video channel and grinned at me.

"Can we have a drink Becky?" he asked.

"I suppose so," she sighed, "pour me one while you are at it."

My grin widened when I saw Peter pour out two thirds of a glass of vodka and top it up with tonic and a dash of lime, he then poured himself and me a quadruple scotch and added some dry ginger mixer. Handing the vodka to our sister and one of the glasses of scotch to me he grabbed his own glass and sat down in his chair, both of us watched as Rebecca took a large swallow of her drink, she coughed and we both thought the game was up.

"You always put in too much lime." She said and we breathed a sigh of relief.

"Sorry." Peter said with a huge grin.

Peter started the tape going, I noticed he had muted the sound, which meant our sister wouldn't notice what we were watching for a while, as long as she kept her nose buried in her magazine that is. I didn't really miss the sound, the action was what held my attention, sipping my drink I watched a woman meet two blokes at a flat, after a brief bit of chat they all stripped and got down to some serious fucking. The film had reached a point where after the woman had sucked the dicks of both guys they were fucking the woman, one in her arse, and the other in her pussy and at that moment Rebecca looked up.

"What the...?" She exclaimed.

Peter and I looked at her pretending innocence; she drained her glass and looked from one to the other of us then shook her head.

"Peter," she said, "Andy, don't pretend to be innocent. You are a pair of sods."

"Aw, come on sis," I wheedled, "we've been watching it for half an hour, can't we at least finish the tape?"

"Alright," she sighed after a moment of thought, "but at least put the damned sound on."

My brother turned the sound on and the room was filled with the noise of a woman screaming with pleasure and two guys grunting as they fucked her. Pleased with myself I settled back to watch the film, but somehow I'd lost interest in it, looking at my brother I saw he was glued to the screen and when I looked over at my sister I was surprised to see her leaning forward to see the action better. It also surprised me to see her hand squeezing one of her boobs, grinning I looked at my brother and gave a quiet cough, he glanced up at me then looked in the direction my eyes were signalling him to look, he grinned and looked back at me.

"She's randy." He mouthed to me.

"She's not the only one." I mouthed back.

We turned our eyes back to Rebecca who was by now crossing her legs tightly; obviously she was getting more pleasure from the film than we had. Suddenly she looked up and noticed us watching her.

"God," she sighed, "what now?"

"Having fun?" I asked innocently.

"What?" She responded.

"Feeling good?" Peter asked emphasizing the word 'feeling'.

Our sister knew we had caught her out, her hands guiltily dropped to the couch and she uncrossed her legs.

"What if I am?" she said defiantly.

"Well we could help you." I laughed.

I'm not quite sure why I said it, probable to get a rise out of her; she looked at me then at Peter.

"You two." she laughed, "Don't make me laugh."

"Oh yeah!" I retorted.

"Neither of you would know what to do if your lives depended on it." She stated with a loud laugh.

"You're asking for it sis." I said.

"Yeah." Peter chipped in.

"You wouldn't dare." She roared with laughter.

Rebecca really should have known better than to say those magic words, then again maybe she did know what she was doing. To my brother and I a dare was like a matador's cape to the bull, the trouble both of us had got into because we could not resist a dare was unbelievable and here she was not only daring us, but laughing in our faces as well. Peter looked at me, I nodded, he grinned, and together we stood up, walked over to our sister and looked down at her.

"What?" she smirked up at us.

We smiled down at her, both of us reaching down to grab one of her arms apiece.

"What?" Becky repeated uncertainly as we pulled her to her feet.

"You really shouldn't have dared us Becky." I said quietly.

"Definitely a bad move." Peter added, "Will you do the honours Andy?"

Our sister was baffled by his words, but Peter and I had an almost telepathic understanding at that moment and I knew he was referring to the buttons on our sister's blouse. I nodded to Peter to indicate that I would do the honours; he grinned and changed his grip on Rebecca's arm so that he could move behind her to take the arm I was holding. At first Rebecca didn't realise what I was going to do, but after I had opened the second button on her blouse and was reaching for the third she caught on and tried to pull away.

"Andy no!" she gasped.

Peter held her firmly while I continued to open her buttons and when they were all open I pulled the material out of the waistband of her skirt then pushed the blouse off her shoulder's. As though we had practised it Peter released his grip on one arm just long enough for me to push the blouse down, renewing his grip we repeated the procedure with the other arm. Grinning I pulled the blouse off my sister and tossed it across the room into my chair, reaching around her I opened the clasp of her skirt then the zip, as I pushed the skirt down her legs Rebecca started to struggle in my brother's grip, but it did her no good. With a bit of a struggle I got her skirt off and tossed it into my chair, reaching behind her again, this time I opened the clasp of her bra and despite her protests and struggles I got it off, it too landed in my chair as I stared at her tits.

After a few moments I tore my eyes away from her tits and pushed at her panties, Rebecca's struggles became more frenzied, but despite this I soon had her panties off and thrown across the room. Taking a step back I quickly stripped off my clothes, Rebecca struggled in Peter's grip, but I noticed that her eyes flicked over my body as I took off my clothes. Once I was naked I stood in front of her for a moment, reaching out I tweaked her nipples and she gasped. I'd known as soon as I'd seen her hard nipples that my sister was turned on yet she was still struggling and protesting.

"Christ Andy," she exclaimed, "don't!"

I grinned at her and teased her nipples again, nodding at Peter I prepared myself to grab her arms, with a sudden twist Peter turned our sister around. Quickly I grabbed her arms and pulled her tight to me, my cock sliding into the crack of her bum. Rebecca struggled like crazy, but I held her firmly, at the same time I enjoyed the feel of her body rubbing on mine, especially the sliding of her backside on my hard cock, over her shoulder I watched my brother strip then reach out to fondle her tits. After a few minutes Peter looked at me and nodded, quickly I turned my sister around, Peter grabbed her arms again and pulled her tightly to him, I moved close to Rebecca, put my hands on either side of her head and held it still.

"Andy..." she started to cry.

I silenced her by pressing my lips to hers, Rebecca surged against me in an effort to get free, but my grip was firm as was my brother's, all she succeeded in doing was rubbing herself on our bodies. Raising my hands to her tits I played with her pliant flesh and teased her hard nipples while increasing the pressure of my lips on hers, releasing one of her boobs I slid my hand down to her pussy and gently stroked it. Becky groaned as I pressed my thumb on her clit, it was the first real sign that she was starting to enjoy what I was doing. Parting our lips I leant back and looked at her face, I smiled as I saw her eyes were closed, her lips curved in a small smile of enjoyment. Her eyes opened and looked into mine I saw desire there, but there was also something else, uncertainty, but even as I watched the uncertainty faded as my fingers excited her pussy and tits.

"Andy," Becky said in a low voice, "please don't."

"Too late Becky." Peter said over her shoulder, "You know that we don't back out of a dare."

She tried to struggle again so I speared two fingers into her pussy, my thumb still pressing on her clit as I thrust my fingers in and out of her tight, wet pussy. After a few minutes Rebecca started to move with my fingers instead of against them, I grinned at Peter, he grinned at me.

"You still want us to stop?" I asked quietly.

"No." she said so low I could barely hear her.

"Pardon?" I grinned at her.

She looked me in the eyes, her excitement increasing as I continued to finger fuck her, her tongue flicking across her lips in a sensual way.

"Don't stop." she said a little louder.

"If we let you go" Peter said, "what will you do?"

Rebecca was silent for a moment, but the longer she delayed in answering the more my busy hands aroused her.

"Whatever you and Andy want." she eventually breathed as she pushed down on my fingers.

To be honest I was a little surprised at her reply, it struck me that she could be just saying what she thought we wanted to hear and as soon as we let her arms go she'd be off.

"Anything?" I asked thrusting my fingers into her pussy.