I hadn't know Judy long, about three months. What I did know was she loved sex. She was like the martini girl, any time, any place, anywhere. But mainly as we were both single and living with our parents it was in the car or in the open. She seemed to get an even bigger thrill if there was a chance of being caught. I also think that as Judy's parents were very religious, it was some kind of rebellion. I didn't really care what caused it, just that it was me that was benefiting from her behavior. It started off as a pretty ordinary Friday night when we met up with our mates and had a few drinks, soft ones for me. Then as the others went on to a night club we peeled of to go somewhere quiet. Judy said that she had heard of somewhere closer than where we normally went and suggested we try it. It was a large carpark behind a large shopping parade. It was only lit near the shops, the rest was in total darkness. We got out the car and into the back seats. I was soon sucking on Judy's tits and her long thick nipples. She was moaning as I sucked her nipples. Then as I worked a hand into her panties she was working on releasing my cock. Then we were down to the real business. We were naked and I was on top thrusting deep into Judy's pussy and she was loving it from the moans and groans coming from her mouth. Judy came long before I blasted my cum deep into her pussy. We rested for a while and then Judy wanted to go again. She was sucking my cock when I noticed movement outside the car. Whoever or whatever it was, was in the dark side of the carpark and just out of view. I still wasn't ready to cum when Judy suggested we get out the car so she had more room to suck me. I told her there was someone out there. She just laughed and told me that it would give them a good thrill. Then before I had a chance to say anything else Judy was out the car and waiting for me. I went back to sitting in the drivers seat with my feet out the door and Judy was kneeling on a cushion sucking for all she was worth. Then whoever it was moved again. I told Judy and she just seemed to suck harder. I was now getting hard again. Judy decided that she wanted me to fuck her bent across my bonnet. She placed herself leaning on the cushion on my bonnet. I positioned myself behind her and thrust back into her hot pussy. I lasted a good ten or more minutes as I banged away at Judy's pussy and she pushed back onto my cock. She came twice and was building to a third orgasm when I came again. Judy groaned as my cock wilted and slipped out of her pussy. I staggered back to my drivers seat. Then I saw our audience. He was a man in his forties. He stepped forward from the dark with his cock fully erect as he stroked it. Judy was still on the bonnet and was rubbing her pussy trying to get to her orgasm. I don't think she even saw him as he stepped closer and then was right behind her. Then he was in her. This man we had never seen before was screwing my girlfriend. He was old enough to be her father, but he was still giving Judy a good shagging. Judy was looking at me through the windscreen, as she groaned at the man's pounding of her pussy. Then I watched as Judy's face scrunched up. I knew what that meant as she then started to shake as she plunged into a huge orgasm. Then he was jerking short deep thrusts into Judy's pussy as his cock filled her with his cum. Then he wiped his cock on her arse and tucked it away and zipped up. Then he disappeared back into the darkness as quick as he had arrived. Judy was recovering and staggered her way to the passenger seat. As she sat there I could see our joint juices trickling from Judy's pussy onto my seats. "Wow did you see that," Judy asked me. "Did you see him fuck me." I told her I did. She was stroking her pussy rubbing our joint juices on her clit. I was getting hard again having watched the most erotic sight of my girlfriend being shagged by a complete stranger. "Fuck me again," Judy insisted, it was an order not a request. She shuffled off her chair and turned with her arse facing into the black night. I was quickly behind her slipping into her wet slimy pussy with our joint juices. As I fucked her I couldn't get the visions of the stranger fucking Judy out of my mind. I slammed Judy's pussy for another fifteen minutes. She came twice more, the second one triggering my own climax and pumping further semen into her already cum soaked pussy. When we had recovered Judy finally put her panties back on to try to stop the flow of cum from her fanny. Then I drove her home. A few days later we talked about what had happened. Mainly that it had really turned Judy on being screwed by a total stranger, and the fact that it also got me very excited watching them. I arranged a couple of mates to be in the carpark and screw Judy on a couple of occasions. It was fun, but not as much fun as the spontaneous fucking she had received that night. We went on to going to parties and swapping. It still never quite matched that original incident. I never did stay with and marry Judy. The wife I did marry, was also into this sort of thing and often picked up men in front of me and and fuck them in public places. Alas she died just a few years ago and I miss all that spontaneous sex.