Where sex was concerned my girlfriend and later my wife was full of surprises. Never conventionally monogamous, neither of us were particularly territorial with each other though I confess I was turned on by her transgressions whereas I suspect she tolerated mine. We were only recently married in the early seventies and had a flat in Teddington. We often went up to town to see bands or get a meal in one of the trendy but cheap bistro's that were opening around Notting Hill. It was after one such outing that the incident I am to relate occurred. After a few drinks in a little pub in Bayswater we sauntered out to the tube. It was a warm July Friday evening. Les had on a blue dress with orange polka dots which fitted her upper body snugly before flaring out to finish well above the knee in a ruffled hem . That and the low cut ruffled neck line gave it a sort of Spanish look I suppose. She was tanned, carried a shoulder bag in the same colour as the dress with white platform sandals. All night long she had attracted plenty of attention. Hardly surprising. Her long auburn hair shone and with her aquiline features she could well have been Spanish or Italian. The dress without being overly snug showed she had the firmness of body appropriate for her twenty two years and her 34a breasts clearly didn't need the help of the lacy push up bra that she wore. Needless to say I felt like a cat that got the cream. It was unusually busy. Whether there was major event on in the vicinity or not I don't know but from being arm in arm we had to put up with holding hands in the crowd on the platform. When the train came it to was pretty full but when you're young it's part of the fun and we allowed ourselves to be carried by the tide of people into the carriage. We were separated in the jostling for a space to stand and could only exchange mouthed messages to each other between the heads and shoulders of our fellow travellers. At Notting hill gate we had the opportunity to get a bit nearer each other but it was no less congested. The train rattled along the circle line towards South Ken. Before we reached Gloucester Road she mouthed something to me and I struggled to lip read. Something about a number I thought. I responded, 'What are you on about?' Her lips repeated their routine. This time with more precision, or perhaps I was keenly attentive. Anyway no mistaking she said "is this the queue for the No47 to Richmond", and raised her eyebrows indicating behind her. This was a bit of an in joke between us. She had come back from a shopping expedition in Kingston one Saturday saying she'd been 'goosed' in the bus queue by a guy. At first she had thought he had pushed against her by accident, but when he persisted in standing close behind her even when there was no crush, she had turned round to give him a warning look. He then blurted out "Is this the queue?" And ran off. Since then if passing her in the confined space of our flat, I had often rubbed my groin against her behind and made the same comment. I stared at her quizzically, mouthing "the guy behind you?" She smirked back and nodded surreptitiously. I was still separated from her by a number of bodies, and was unsure what to do. Silently I questioned, "Are you ok?" She responded with another smirk this time unmistakeably lascivious and "I'm enjoying the attention!" I was to say the least bewildered. When the Kingston incident happened, she had been rightly indignant at the bloke's presumption that he could get away with touching her up uninvited, in public. Now, well who knows what she was thinking. At least it resolved one issue. I wasn't in the immediate situation expected to throw someone off the train. I turned my attention to man behind her. Difficult to judge his age. Like many city types of which I guessed he was one, he held a copy of the Standard in his strap hanging hand which partially obscured his face. His posture was straight, taller than me maybe 5'-11" (putting his tackle I estimated on a level with Les's behind), his hair showing some grey probably meant he was in his late thirties. It was not possible to make anymore ground toward Les until the doors opened at South Ken. With some manoeuvring I was able to stand right I front of her. The city gent made no move but then neither did my wife. The doors closed and the rumbling train accelerated into the tunnel. I stared at him over her shoulder. He was, about forty, clean shaven and looked impassively at his paper, nothing in his expression indicting anything untoward was at hand. I noticed his raincoat, worn no doubt over a pin stripe suit, was open and effectively provided a screen either side of Lesley. She had adjusted her position and was now holding the same strap as him. They rocked together with the roll and pitch of the carriage. Whispering to her again, "You ok?" I was told in a breathless tone, "I can feel his prick rubbing against my bum." "You don't mind do you? It's just a laugh really." Even if I minded on one level, my cock was already twitching at the knowledge of what she was allowing. Edging closer to her but not wanting to make her molester aware of our connection I placed a hand on her hip and was shocked to realise she was gently flexing her buttocks against this strangers cock. He was backed up against the partition to the door access area. Les in front of him, left side to the doors her left hand clutching her bag. Their closeness suggested they could have been a couple or maybe not to the casual observer. I was both concerned that she should not be exposed in public but wanted the assault to continue, so placed myself to further obscure them from other passengers. As the train slowed into another station I was aware of Les shifting her stance, placing her feet slightly apart. Momentarily her eyes closed and she bit her lip. Then her expression resumed its composure. She smirked at me, I lip read. "his hand is in my knickers" My cock was straining in my pants imagining the city suit's fingers surreptitiously sliding under the elastic of her white broderie anglais pants and probing my wife's fanny. My attention flitted from her to him. Neither of their faces betrayed the intimacy of what was apparently happening between them though Les' face had that look of distant concentration I had seen sometimes when she was trying to control the build up to a climax. The only change was that somehow the guy had disposed of his Evening Standard. Screeching and squealing the train stopped and the doors opened. We were at the Embankment. Our Stop. I looked at my wife and said, "It's our stop." She was motionless for a second then stepped away from her clandestine partner. She followed me onto the platform without looking back. As we came through the barrier, she began to giggle. "He had his cock out between the cheeks of my bum." "You dirty sod!" I laughed back. "Would have let him fuck me?" she asked. "I would have watched you as well," I replied. "Well, you're a dirty sod too then." And we held hands and joined the homeward crowds on the embankment pavement. As we paused to cross the road to take our usual goodnight look at the river, I looked over my shoulder. The city gent was standing watching us from the entrance of the metro station. I told her, "Your boyfriend is following us." "I don't want to see his face," she whispered, "that would spoil it." She led the way. Crossing the road at a convenient break in the traffic, then up the steps to the Hungerford footbridge to Waterloo. As we reached the first landing I saw the man take the first step in our wake. In a few seconds we were on the bridge. As usual it was gloomy, with patches of heavy shadow where the lighting failed to reach. Some people avoided it after dark but we had always enjoyed the view of the river from here and the distant buildings lit up. There were few people about not even the drunks who occasionally begged for a bob to buy a 'cup of tea'. Somewhere towards the middle, at a spot palely lit by an overhead lamp Les stopped and looked out over the river. Her chin barely cleared the parapet of the bridge. "I want to let him have me. You want me to, don't you? Will you wait a little way further up the bridge?" I nervously nodded. "Ok but I'll keep you in sight," and walked slowly towards the Southbank. From where I stood I could see Les, bare armed, hands on the parapet facing the river looking towards the Southbank Centre. Even in the milky light her white shoes stood out and her brown legs seemed to shine, but maybe that's my imagination. I watched as the city type emerged from the distant darkness through a well-lit patch, his pale raincoat illuminated by the weak light and walk up behind my wife. Both of his hands slipped under the hem of her dress, and there was a momentary flash of white as he tugged her knickers down her legs. Her dress was up round her waist as she stepped out of the flimsy pants. Then she was enveloped by the folds of his raincoat as he stepped in close. A couple arm in arm, giggled as they passed then looked disapprovingly at me, judging correctly that I was a voyeur. I could see his right hand was foraging up around her front. He leaned back, I heard the zip hum, and she dropped her arms. The dress slid off her shoulders. She returned her hands to the parapet and kept her gaze over the river as his fingers pushed her bra up out of the way and mauled her small hard breasts. From behind me a group of lads sauntered through, sniggering they shouted to the city guy to "give her one for us" but continued on their way. The city gents left hand was deep into her crotch pulling her into him no doubt parting her downy pubic hair and reaming her cunt. For the first time in their encounter I could hear Les murmuring. Relinquishing his handling of her tits, city man's hand dropped to his groin. Les' body was revealed for a few seconds naked except for her dress, bunched around her hips and the white of her bra like a scarf above her pert breasts. He was clearly positioning himself and bent his knees before thrusting his groin forward. My wife accepted his lunge, hands on the parapet legs akimbo and backside presented perfectly for his cock to have no resistance. Briefly he paused, his groin and her behind snug together, before commencing to fuck furiously. Resuming his fondling of her breasts, he grunted as he rammed into her, forcing her against the wall of the bridge, his left hand continuing its ministrations at the front of her fanny. Though she had had sex with other blokes before and since our wedding last year, sometimes with my encouragement, this was the first time I'd actually been there. I watched and felt my cock leaking cum into my pants. "He can't last much longer," I thought. At which point his frantic assault stopped and half a dozen convulsive jerks indicated he was shooting his load .For a few seconds he held on to her then stepped back. I saw his prick still half hard. He wiped it on her behind, zipped up his trousers and walked off in the direction of the embankment. As I walked towards Les, I thought how disgustingly sexy she looked in the lamplight. Her dress still around her hips and sperm dripping down the insides of her thighs. I wanted to fuck her right there, but she had pulled down the hem of her dress and I judged for the moment it was best to leave her alone. She rearranged her bra and I zipped up the dress. We walked in silence to our train at Waterloo. Luckily we had a compartment to ourselves. "That was pretty wild," she said. I agreed. "Did it turn you on?" she asked. "I came in my pants," I admitted. "Well then, you can make me come now," she laughed pulling the hem of her dress up to expose her cunt, pubic hair matted with her lovers spunk. My dick was already stiff, as I pulled her onto her knees in front of me and slid my hand under to part her cunt lips. It slid into her easily. Suddenly I was hammering at her with the same ferocity I had seen from the city gent only half an hour ago. "It really turns me on when you're dirty!" I gasped. "You are such a filthy slut." Pausing only when the train pulled into stations we fucked all the way back to Hampton Wick.