She was in a big group, and I didn't notice her at the start-line.
It wasn't till about the half-mile point that the runners gradually separated-out into their classes - dedicated athletes upfront, then the keen amateurs, and lastly the clowns, just in it for a laugh. She and I were in the middle group, and she was proving to be slightly faster than me.
It was cold for the time of year, and I'd put on a heavy track-suit. She'd compromised with tight-fitting pants that reached to the knee. The sight of that discreet, trim butt-end jogging up and down in front of me was something mesmerising. And I didn't want anything to come between us, as you might say.
But that's rather hopeful when you're somewhat out of training, and I found I was having to struggle to keep her in sight.
Just before the one-mile marker, there was a tight bend in the track, and as she swung left ahead of me, I was able to see her face for the first time.
She looked rather a serious type with a sharp little nose and a deep, ruddy complexion. The black hair was short, but well-styled. I think I was almost glad she wasn't a conventional glamour-girl. That didn't diminish her appeal one bit.
But right now, she was heading right out of my life at a mighty rate of knots. I cursed all those beers and late-night curries that were slowing me down, and f***ed myself to try and step up the pace. It didn't last. Another bend, and she was briefly hidden by some trees. By the time I caught sight of her again, she was just a distant shape, and I knew I'd lost her. Three miles later, I had finished well down the list, defeated and demoralised. There was something symbolic about losing my fighting edge, and losing her too.
Like most of the other fellows, I could do with a slash, so I filed into the crowded little marquee with the 'Gents' sign outside, for a burst of highly welcome relief. Emerging into the park, I noticed three long queues of women-runners, waiting their turn at the portakabins they had to use - one of those times I thanked God I wasn't a woman.
And suddenly there she was, quite near the back of her queue, looking miserable and fit to burst.
I went up to her and pointed to a small grey bungalow just three doors down from the park gates.
"Come on. You can use my bathroom if you like."
She nodded her thanks, though without the smile one would expect. But I'd already figured she wasn't a fun type. And now, incredibly, she was coming with me, looking uncomfortable, moving a little awkwardly, weak bladder perhaps.
Well, it's a good thing my bathroom's on the ground floor. We just shot in there, and it was obvious she was in a heck of a hurry.
It just seemed natural to help her off with the clingy pants, and to seat her on the pedestal.
Her relief was so intense, she seemed to be in a religious trance, eyes closed in some kind of divine ecstasy as she sighed-out her pleasure.
For me, it was a first - hearing that sweet water-music from the golden droplets tumbling from her little fountain. And I was finding it a heck of a turn-on - first time I'd risen to the occasion so quickly after a hard run.
I risked placing her hand on it, and sure enough she kept it there. This was a completely different person from the severe, rather feminist-looking character I thought I'd identified out in the park.
Now the music was tailing-off and I gently touched the little fountain, and then the lips of her arse. She gave a surprisingly violent shudder. So I held her and pulled her down on to my new, soft bathroom carpet, where she began to devour my prick greedily, even painfully, as I arranged the rest of her over me, in the classic 69.
It was truly wonderful tasting her last droplets of liquid gold, and then the glory of her shithole - all her magic juices running and blending together, as more and more sweat ran off her unwashed body, and I sucked and sucked until her low moaning told she was ready.
Nimbly, like the athlete she was, she knelt up and eased herself backwards on to my prick, and we found our rhythm. The sounds she made were not words. They were thoughts and feelings, but not words. In fact, she had never actually spoken a word - obviously wanted this to be some kind of ballet. The only time I've ever made love without words - a mysterious and poetic experience.
But soon after she climaxed, dull reality intervened, as she reverted to her normal self. Of course, she had to be off, didn't she?
Just one tender look in my eye, and her finger across my lips. Then back to her everyday world, of which I am doomed to know nothing.