He found himself basking in a kind of erotic nostalgia as he dressed. Sylvia was a cracker and a real nympho but it was like eating the same kind of exotic food every day of the year. You didn't actually come to dislike it but it got boring, so you decided to try a change and then came back to the original refreshed.

That had happened to himself. And Sylvia. Thirteen years ago, two years after they had married. It had had a most unlikely beginning, like taking a seemingly harmless drug and then before you realised it you were hooked on it.

Alan had been the root cause; if it hadn't been for Alan, he and Sylvia might have spent years struggling to stay faithful to each other and then broken up. As it was they were still together and the relationship did have its rewards. Tonight was one of them.

Alan's wife had left him for another guy and poor old Alan had been pretty cut-up. That was why they had started inviting him over on Saturday evenings for dinner. Maybe it was the drink that triggered it all off, had them casting their inhibitions overboard and telling dirty stories. Sylvia was the worst, Eric winced, wondered where the hell she had heard them all, but after a bit he didn't care. None of them did.

Alan began bemoaning the fact that he hadn't had a woman for three months, almost cried. So frustrated that he was toying with the idea of having a week in London and spending his nights in Soho. That was when Sylvia had come up with her offer, straight out with it like she might have been asking Alan to go to the club with them next Saturday night. 'How would you like to screw me, Al?' She was deadly serious, a genuine offer. 'I know Eric won't mind, not just this once, will you, Eric?'

Suddenly everybody had sobered up into a stunned silence, all eyes on Eric. Well, Eric, you won't mind, will you?

No, I don't mind, not at all. You fuck her, Al, leave her lying up there on the bed ready for me when you've finished. Sylvia and Alan drained their glasses, went out of the room. Eric poured himself a stiff brandy with a shaking hand, found himself listening to them moving about in the bedroom directly above the dining-room, pictured the scene. Sylvia couldn't wait to get everything off, she was always like that, Al maybe nervous and losing his initial erection, having difficulty getting it up again.

It wasn't fair to eavesdrop on them. Eric heard the bed creak the way it always did when you got in, stood up and walked unsteadily across the room, switched on the stereo. A slow rhythm on the first track, speeding up on the second, just like those two upstairs.

God, this was the ultimate in eroticism, everything he had ever fantasised about coming true in one electrifying session. He wondered if Sylvia had ever done it with anybody else since they had been married. He told himself she had, she must have; he wanted it that way. Those nights when he was away . . .

He thought maybe the clock on the mantelshelf had stopped, stooped and put his ear up against it but couldn't be sure over the music. 12.10. Christ, they'd been up there an hour and a half, Al was really giving Sylvia a banging, making up for everything he had been forced to go without over the past months.

It was 12.35 when he heard Alan go, footsteps in the hall, the front door closing softly, a kind of guilty click. In a way it was a disappointment, his best mate slinking off, not wanting to face him. Sorry, Eric, I've screwed your wife and I feel pretty bad about it. Don't, Al, it's been a great evening. For me, too.

Sylvia hadn't had enough whatever had gone on, that much was plain. When Eric entered the bedroom she was lying on top of the quilt, legs lewdly spread, a small damp patch on the material between them; eyes closed, ecstasy not guilt.

He went straightway to her, no preliminaries, pushing right into her, feeling the liquid warmth of adulterous seed. God, what a night, he made it twice, almost a third time. If ever he needed a fantasy for the future then this was it.

Three or four times after that Al came round and it got to be a Saturday night routine. Too much of a routine probably, too clinical, and nothing could ever match that first night. Then Alan found himself a girlfriend, moved in to live with her and that was the end of that. But Sylvia had had a taste of the grass on the other side and she wasn't going to let it drift away like that.

He wondered to himself now as he sat on the edge of his hotel bed just who had set up that relationship with the Joneses. They had known George and Marie for two or three years but it had never been more than a casual dropping in on each other at infrequent intervals. Then one Friday when Eric returned home Sylvia seemed more vivacious than usual, told him that they had been invited over to have a few drinks with George and Marie the next night. Nothing to get excited about but Sylvia certainly was. He sensed then that something was in the air. No, it couldn't be, the Joneses were far too conventional, even went to church some Sundays. Unless Sylvia was casting her line for George; Eric wouldn't put it past her. But he was curious enough to want to find out.

It was damned funny the way that evening had trickled on into the early hours before anybody (Sylvia) made a positive move. Half-innuendoes became innuendoes fired by a cheap bottle of Scotch. The Joneses couldn't really afford drinking on this scale; George was on the dole and he wasn't the type to go moonlighting. Too honest, too bloody conventional. Except when Sylvia and Scotch got to him.

Sylvia engineered it all, nobody actually came right out with it and said, 'Shall we swap, then?' Somehow she got herself on to George's lap in the armchair and left Eric and Marie together on the settee. A lot of couples change over for a bit of snogging when everybody's had too much to drink, Eric decided, didn't dare try for a feel. It would all fizzle out before long, and then the party would break up; he didn't want to make a fool of himself.

Out of the corner of his eye he saw George and Sylvia slipping out of the room, heard them going upstairs. There couldn't be any further doubt, Marie was expecting him to play his part in this sexy foursome.

She was OK, a bit nervous at first, then he broke through the barrier and she exploded. In fact, she couldn't get enough, unbottled every inhibition which she had ever had during the next hour. But it wasn't her that was turning him on like this, had him achieve that elusive third orgasm. It was the knowledge that Sylvia was upstairs revelling in another session of red-hot infidelity.

It was funny how they never swapped with the Joneses again after that night, never even called round for a quick drink, didn't even get a card from them at Christmas. Something had gone wrong somewhere along the line. Maybe Marie had had a fit of jealousy in the cold sobering light of a November Sunday morning.

And Sylvia seemed to lose her enthusiasm for the way-out scene too. Just like that, a marital screw at weekends but she didn't even try to lure Eric into anything else. He even got to thinking that she'd had her wild fling and had decided to resign herself to the dull routine of a straightforward marriage even though they were apart five nights of most weeks.

Then rumours trickled back, a muddled jigsaw that needed a lot of piecing together. In remote rural areas, it was true, the last person to hear stories concerning one's wife is oneself.

It was that nut up at the organic farm who was shagging Sylvia. It figured. It was funny how Eric experienced a pang of jealousy the first time he found out for sure. If it had been Al or George it wouldn't have mattered. They were ordinary guys who just wanted a fuck, nothing more, a thrill to boost their own marriages the same way that Eric needed one now. It ended when you came, as simple as that. But this fellow was different. His wife was a flighty bit of stuff, if all the stories about her were true, going off on her own at nights to nightclubs and doubtless getting herself shafted. The ice was dangerously thin in that quarter.