This is a true story.

My sister had been visiting and staying with my wife and I for 2 weeks now, and I was starting to get a little restless. The problem was that with somebody else in the house, there did not seem to be much time for sex with Zoe, my wife. To compound the issue, I had always secretly fancied my sister, and seeing her walk around in her night gown in the evenings, with her firm nipples pressing against the thin fabric, was just making me more turned on.

She had grown into a really sexy woman, with E cup tits (I had looked at the label on her bra in the laundry hamper a few nights earlier). She also worked out a lot, and had a lovely flat stomach and a firm round ass.

Every evening she would walk around the house in a pair of thin, almost sheer pyjamas that clung close to her body, so close that I could easily make out the smooth outline of her vagina, clearly clean shaven as the smooth profile of the fabric revealed. I am sure that she had noticed me staring at this more than once while she moved through the room, but she never let on.

Anyway, tonight was special. Tracy, my sister, had gone out to meet an old friend from school, and Zoe and I were alone in the house for the first time in 2 weeks. We had been sat in the lounge watching a movie, but I could not really contain myself, and after only a few minutes, I had slipped my hand down Zoe top, and started to gently roll and tug on one of her nipples. At first Zoe just carried on watching the movie, but after a few minutes she let out a little moan

“Mmmm, that feels good.”

“Well why don’t you get your top off so that I can get at them better”, I said.

“But what about Tracy?”

“What about her, she is not here, and won’t be back for hours yet”

“I guess” she said quietly, and she slipped the T-shirt off over her head. She had not been wearing a bra, and her tits jiggled a little as she settled back in the couch.

Zoe had a great pair of tits. A nice solid C cup, with small but firm nipples that were just begging to be sucked. We had not had any children yet, so her tits were still young and firm. I moved close to her on the couch and put my lips over her nipple and started to gently stroke it with my tongue, feeling it grow firmer with each stroke. My hand moved over to her other nipple and started to gently pull on it, lifting her breast slightly with each pull. As her nipple grew harder, I pulled slightly harder, holder the whole weight of her breast for a few seconds at a time.

I knew she liked a little nipple pain, and while my hand tugged at her nipple, I started to gently bite on the other, getting a little more aggressive with each pass, until I could hear Zoe making little gasps and shudder with each bite.

Suddenly she lifted her hips and quickly slid her skirt and panties off and dropped them at her feet, then slid her hand between her thighs, and started to stroke her slit slowly, which was already wet from my nipple play.

Once her fingers were well covered with her juices, she moved her hand up to her breast, moved my hand away, and started to tug hard on her own nipple. This was how she always liked it. As she tugged she said:

“Don’t stop; keep biting gently on that one.”

By now the nipple in my mouth had grown rock hard, and her breasts had become slightly firmer from her arousal. My dick was also now rock hard, and straining at my shorts. I just had to let it out, so that Zoe could start stroking it with her free hand.

“Wait a moment,” I whispered “I just need to get these shorts off.”

I sat up on the couch and turned to get up and remove my shorts, and as I did so I froze with surprise. “What the hell! What are you doing here?”

It was Tracy, standing there staring at us. Zoe’s eyes popped open to see what I was talking about, and seeing Tracy standing there she grabbed her skirt up of the floor and tried to cover herself with it (rather unsuccessfully).

“I’m sorry,” said Tracy, “Brian stood me up, so I decided to just come back home. I walked in a few minutes ago, you obviously didn’t hear me.”

I was a little shocked and not quite sure what to say or do. Zoe just sat silently, looking very uncomfortable.

We sat silently for a few moments, not sure what to do next, when Tracy broke the silence, “Can I join you?”

“What!?” I said, my eyes wide with surprise.

“Would you mind if I joined you?” she repeated.

My mind started racing. Was I dreaming, did my sister just ask if she could join my wife and me for sex! This was just too amazing to be real, surely not. My dick, which had lost its erection at the unexpected sight of my sister, was now rock hard again. I glanced over at Zoe, but she said nothing, she was just staring at Tracy, still clutching her skirt against her body.

I turned again to look at Tracy, and before I could say another word she started to unbutton her blouse and move towards us.

“Ummm, I don’t know...” I started to protest, but I was cut short as I felt Zoe hand squeeze my thigh. I looked over at her and saw her eyes were fixed on Tracy. My heart started pounding in my chest, so hard I felt sure Zoe must be able to see it beating! Was this real!?

My gaze returned to Tracy, “What are you doing? Why are you doing this?” I asked.

By now Tracy had removed her blouse and I could clearly see her breasts bulging out of the small lacy bra she was wearing. My god! How many nights had I laid awake wishing I could get a look at those tits. Tracy was older than me. When I was 13 she was 15 and already fully developed, and as a teenager I had often lain in the bath stroking my cock imagining what they must look like, and now here they were, about to be revealed to me.

I looked back at Zoe, convinced she would get up and leave, probably run to the bedroom and close the door, but she was just sitting there staring at Tracy. I turned back to look at Tracy again. As I did so she reached her arms behind her back and released the clasp on her bra, and let it fall to the ground. There in front of me were her huge, perfect breasts. They were more perfect than I could have imagined, with large dark nipples which were already standing erect. She moved forward towards Zoe.