It happened back in the summer of 1985.
At that time my sister-in-law, Clare, was recovering from an operation for the removal of a benign brain tumour. Clare is my wife Sue's elder sister and, in an attempt to aid her recovery we had invited her to spend a week with us aboard our canal boat "Gemima". We planned to cruise a particularly remote section of the South Oxford Canal and during the early part of our trip it seemed to me that Clare was behaving in a rather uncharacteristic manner: she seemed more demonstrative than usual, almost clingy, but also had a tendency to become snappish or to lapse into long, brooding silences. I mentioned this to Sue who told me that Clare had confided to her the fact that since her operation -- and possibly, also, as a result of her recent divorce -- her long dormant libido had quite suddenly become inflamed to an alarming degree. Masturbation, it seemed, could only partially satisfy her needs
"What she really needs is a darned good seeing-to", was how Sue rather crudely put it.
I was surprised by this news as I had always imagined Clare to be the sort of woman who tolerated sex rather than enjoyed it, indeed I believed this to be one of the reasons for her divorce. She was in her middle forties, a little plump and, whilst certainly not unattractive I had never thought of her as having sex appeal. Admittedly she had nice legs and a well-developed bosom but her general demeanour had always seemed to me more redolent of the vicar's wife than the village flirt.
A few days later Sue repeated her remark about Clare but this time it was accompanied by a shrewd look and the meaningful comment, "what about it?"
I confess that I was staggered. It appeared that my wife was actually encouraging me to have sex with her sister.
"What about you?"
"Oh, I won't mind," a knowing look, "as long as I can watch"
"Let's be quite clear about this: you are saying that you wouldn't mind if I fucked your sister?"
"No, because I think it would do her a power of good. Actually I think you might even enjoy it too. After all, it would give you a bit of variety, wouldn't it?"
It took me a few moments to absorb the fact that my wife was not only permitting but actually encouraging me to have sex with my sister-in-law. Not only that but she was proposing to be present while it took place and actually to "help", whatever that meant! Sue and I had had plenty of enjoyable sex together but it had always been entirely straightforward and conventional without a trace of "kinkiness". This proposal was something completely new, but I must confess that the idea was strangely exciting and, to my surprise, I found that I already had an erection.
After a few moments I said, "But how will Clare react if I suggest it?"
"Don't worry about that, she's desperate. I'm surprised you haven't noticed, men usually do. Besides she's always fancied you."
"Really?"
"Oh yes. Look, leave everything to me," she even sounded as though she was enjoying this, "you take the dog out this evening as usual and when you get back I'll make sure she's ready for you."
"Okay, but just one thing," -- I was a little hesitant -- "I've always thought of Clare as belonging to the long cotton bloomer brigade...