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...
Sue knew the powerful erotic charge that underwear has always had for me and quickly replied, "I think you might be quite surprised at what she wears underneath those prim little dresses. Don't worry Darling, I know what you like and I'll make sure she's suitably dressed -- or should I say suitably undressed."
Supper that evening was a little tense. I realised that Sue must have told Clare what was going to happen. I was uncertain whether to broach the matter myself but eventually decided to wait.
After supper I went to get my walking gear on while Clare began the washing up. As I moved back along the boat I came to the narrow galley section. She was standing at the sink and thus slightly obstructed my passage. She took her hands out of the water and pressed her stomach against the sink to let me past. My pelvis brushed her bottom and I knew she must be able to feel the lump in my trousers. Almost without knowing what I was doing I slipped my hands under her arms and cupped her breasts. I expected a reaction but she just stood there with her rubber-gloved hands dripping into the sink. I started gently fondling her and after a moment she sighed and murmured, "Ooh don't do that too often or you'll get me all excited."
I nipped her neck and whispered, "that's the idea idiot."
I could she Sue watching. She gave me a wink and then said, "for goodness sake leave her alone and go and take the dog out. We want to get ready for bed."
We were moored in a very remote spot and the night was a clear one. On my way back I was in a state of excited anticipation but I saw steam issuing forth from the shower outlet on the boat so delayed my return to give the ladies time to complete their preparations.
When I judged that I had given them enough time I settled Monty, our lurcher, in the back cabin, took my boots off and made my way round to the front entrance of the boat. I knocked and Sue cautiously opened the door a couple of inches to make sure that it was me (it would certainly have been embarrassing had it been a stranger!) then opened it fully to let me in.
Sue was wearing her silk housecoat but I was pretty sure that she didn't have a nightdress on underneath. But it was Clare's appearance that stunned me. She had on very dark, very sheer stockings held up by a white suspender belt, a white bra of more than usually revealing design and a gorgeous pair of white, lace-trimmed knickers -- not at all the sort of thing the vicar's wife would wear.