One day, my younger step-sister came to visit while my wife was out. I left the room to get a drink and when I returned, she was sitting on the edge of a table with her hand between her legs. I asked what she was doing and she replied that it should be obvious; she was feeling sexy and was doing something about it. She said she would stop, but feeling my own growing excitement, I said she could carry on. As she continued, I got hotter and hotter. She told me to come close and watch. Finally, she said I should drop my clothes and do her. I knew it was wrong, but did not wait to be asked again. I was going hard when in walked my wife. We stopped not knowing what to do. She just pulled her panties down and sat on the table as well. Raising her dress, she started to pleasure herself and then leaned over and kissed my step-sister on the lips. She then told us to continue, but said to save some as it was her turn next. After doing both of them, I sat exhausted and watched as they pleasured each other. What a day. It never happened again, unless my wife and sister have met secretly, of course.