We had been married about 9 months and had become friends with a guy I was in the service with. One weekend he and his wife asked if Lisa and I wanted to join them at a mutual friends house for a swimming party. We had a great sex life and really had never talked about swinging before that. When we got to the party i had on my regular swim trunks and Lisa had on her modest bikini. We were both virgins before we married and had never been around nudist before. We were surprised when we got in the back yard and a couple of the ladies were topless. Lisa looked at me and blushed and i smiled at her. our host told us that this was a clothing optional party and there was no pressure to join in the nudity so relax and enjoy the party. We had a couple of hot dogs and, a couple of drinks, Lisa was nervous and had a few too many drinks. as the party progressed more and more of the guest were in various states of undress. Lisa could see i was getting really hard and it was hard to hide under my trunks, but I never made a move to take them off, but she with the drinks and a little urging of one of the ladies had taken her top off. She was a small 28b cup and the men were amazed at hoe perky her tits were. She started to get attention from a couple of the guys and it was turning me on. She seemed to be liking the attention and I did nothing to stop it. As the evening progressed I noticed a couple of the couples had disappeared for a while and then came back outside to join the celebration of the 4th of July. Lisa and i were sitting in a chair talking to the hose and another couple when she asked where the bathroom was. One of he ladies who i had learned was Patty tole her she would show her and they disappeared in the house. Patty came out and we were enjoying the fireworks and one of the guys got up and went inside. I started to get concerned when Lisa did not come back out so i went inside to check on her. I walked in the hall and hard a noise from the bedroom. The door was open a little and i peeked in. At first i cold not see who was on the bed under the guy who i found out was Patty's husband. he was really plunging his hard cock into her and she was moaning and enjoying it to the fullest. I was amazed at the way he was plunging into her and how big he was. I was getting rock hard and knew it was wrong to watch and had forgotten about checking on Lisa and i noticed that he was starting to jerk wildly and the lady under him was arching her back and making some strange sounds. It hit me all of sudden who she was when she jerked wildly too and yelled out my name. I was shocked and excited but could not say anything . I went back outside and Charles asked me where Lisa was i told him she was almost finished and would be back in a few minutes. /when she returned I acted like nothing happened and kissed her passionately.