I'd been living with my girlfriend Ann for a couple of years. We had a nice 2 bed flat in a converted Victorian house in a trendy part of town near to the local university. Ann had a sister, 2 years younger aged 22 called Emma. Emma had been living with her parents but had just got a place at our university. Rather than rent a place or move into halls of residence Ann suggested that Emma could stay with us in our spare room for the first year of her studies.
I was fairly relaxed about the idea as I got on well with Emma and she was very easy on the eye. Despite being sisters they were nothing alike physically. Ann was brunette about 5-7 tall and a size 12, whereas Emma was a petite blond 5-2 tall and just a size 10.
Anyway, Emma moved in and things continued generally as normal other than there was sometimes a queue for the one bathroom and there were more discarded clothes strewn around the flat. Untidiness was something both sisters did share in common. It seemed almost every day I found discarded items laying around including some very skimpy erotic lingerie which Emma seemed to like wearing.
I did wonder if having Emma in the spare room next to our bedroom would curtail some of Ann's bedroom behaviour. The wall between the two rooms stopped short of the ceiling to allow some borrowed light from our room which was naturally lit, into the second room, which didn't have its own window. Whilst this allowed a good amount of light, it also meant you could hear everything in each room.
Ann was very vocal when we had sex, beyond the average gasps and groans, often demanding that I 'fuck her harder', or 'shoot my cum deep inside her'. I very much enjoyed talking dirty during sex, but now that Emma could hear everything I thought Ann might be more subdued. But it seemed the opposite was true and Ann seemed to be even louder when she knew Emma was in her room.
Ann was also quite submissive and I would often spank her, especially when fucking her from behind. I loved to land a flurry of hard spanks to her bum just before I came. Ann would always encourage me to spank her harder and make her ass red.
So we continued fucking as normal, even though Emma could hear our every move, especially when I spanked Ann. I'm sure Emma was getting turned on listening in to us as I could often hear little gasps and the rustle of bed clothes after Ann and I had stopped fucking. Nothing was ever said between us, even though we both knew we were listening to each other.
I knew Emma had a new boyfriend called Gary and we'd been out together as a foursome a couple of times. I thought he has a bit old for her and a bit stuck up, but she seemed to like him and began spending more time at his place, certainly at the weekends.
Then one-day Emma asked if Gary could stay over for the weekend because the heating had broken in his house and it was freezing. Ann and I were going away to a wedding and would be staying for the weekend so I said yes and told her to enjoy herself!
We left early on the Saturday so we missed Gary arriving. The wedding and reception was great and on the Sunday Ann accepted the offer from an old school mate, who was also at the wedding to stay on and go shopping with her. The school mate had offered to drop Ann home after shopping, so it meant I could miss the shopping and get home first.