The first slide, a picture of that anonymous red-brick building in the suburbs, brings the events of that second morning rushing back to me. He had picked me up at the motel, and was meant to be taking me to the location for the morning, a secluded wooded area, where I could play at being a slave, held captive in the forest by some deranged psychopath. Plenty of scope for outdoor nudity and bondage against trees and suchlike, I thought.

I had hardly slept the previous night – excited memories of the day's activities, fevered anticipation of the day to come, frequent bouts of masturbation, had seen to that. So I was dozing in the car, thinking about how I wanted him to tie me, how he might shoot the pictures, and not paying much attention.

When we pulled up outside the club, all my wild fears of abduction and abuse came flooding back, but this time with the distinct possibility that they might be well-founded. He turned to me and explained this was the club he'd mentioned to me, the BDSM club owned by his friend. After the previous day, and me saying how I wanted to experience it all, he thought I might like to have a look for myself. No pressure, I could just watch the show, if I wanted to join in, that was up to me.

I have never been so nervous in my life. The second picture in the set is a picture of Dave, the owner, standing behind the bar, big grin on his face. He'd said he was happy for me to take a table and stay as long as I liked, his customers weren't used to seeing a pretty woman in the audience, but they'd cope. If I wanted to be 'part of the act', as he put it, all I had to do was tip him the wink and he'd organise it.

I don't know what a BDSM club looks like, but that wasn't what I'd imagined. I'd been to Ronnie Scott's Jazz Club, and this wasn't that different – long bar, a lot of tables on the floor and booths by the walls, and a small stage. There were no big wooden frames, chain or whips around, just a couple of poles on the stage. There were less than a dozen customers as I sat down with my mineral water, but then it was only 10.30 in the morning.

There's a shot of me, watching the stage, looking nervous. Then one of the girls, the first act on stage. Two young women, somewhere between 18 and 25, dancing around on the stage, wrapping themselves around the poles. The only concession to BDSM seems to the leather and rubber costumes they are wearing. I wonder if they only do the serious stuff later, when more customers are in.

The girls on stage are kissing in the next picture. I remember looking around, feeling lost, wondering what I was doing here, among all these seedy men, with nothing better to do on a weekday morning but ogle a couple of girls pretending to get heavy. I saw the manager looking at me, the smile still on his face, his eyebrows up in a questioning gesture. In response, I waggled my head from side to side, in the international sign for indecision. But who was I fooling? I hadn't come all this way to cop out and run away. I inclined my head slightly, and I saw his smile widen.

The next slide shows the two scantily clad girls leading me up onto the stage. I had been taken by surprise, expecting some backstage briefing, rather than to be gently pulled from my chair and taken up. They had turned me to face the sparse audience, who looked interested in this new development, while they unbuttoned my blouse, easing it off my unresisting shoulders. I click the mouse to see a picture of me standing in the middle of the stage, the girls flanking me on either side, one holding up my blouse, the other my skirt and bra. I am covering my breasts with my arm, but in the next picture, my arms are high and wide, held there by straps on the poles I hadn't noticed before. The crowd had given a generous round of applause as my breasts were uncovered, their first 'topless' action of the day.

In the subsequent slides, my ankles are also strapped to the posts, forcing me into a spread-eagle; one of the girls straps a ballgag into my mouth; ropes appear around my breasts in a harness, constraining and to some extent, supporting them.

Through all of this activity, I was in a daze, barely able to take in what was happening to me. I could feel the women running their hands over my body, pulling my panties up between my buttocks, exposing my cheeks, massaging my breasts, running over my back and stomach. I was struggling to come to terms with the feelings this was engendering in me, feelings of lust and arousal. The next slide shows the back of one of the girls, Charlotte as I found out later, on her knees in front of me. At that moment, her tongue was pressing firmly against the front of my panties, which were rapidly becoming damp from inside and out. The look on my face, staring down at the girl, is one of surprise, mixed with desire. I had never considered myself to have even the slightest lesbian tendency, but this experience has made me think again.

The next picture shows the other girl, Anna, draping a multi-fronded flogger over my shoulder. Now, I look genuinely frightened at the prospect of being whipped in front of a distinctly enthusiastic audience. In the most dramatic picture of the set, Anna and Charlotte are standing on either side of me, one with her flogger held high, the other in the act of bringing hers down across my breasts, the fronds a blur as they lash my body. My face is screwed up in anticipation of the searing pain about to course through my body.

I smile at the memory. I was genuinely scared at that point, convinced I had been duped into taking part in a violent S&M scene, with me as the victim. As I discovered moments after that photo was taken, the 'leather' floggers were actually made of some very soft material, and it was actually about as painful as being whipped by strands of cooked linguini. Suddenly, the thrashing I had been dreading had turned into a rather sensuous stroking of my naked body, continuing what the girls had started earlier. But, in the pictures, it looks genuine, and it must have looked like an authentic beating to the audience as well, as they hooted and clapped in appreciation. They must have thought I was a complete pain slut, as I am clearly enjoying myself in the pictures. The memory of that time is now making me aroused again, and my fingers are back at work.

The stimulation is taken up another level in the next photographs. Anna has donned a strap-on dildo, and Charlotte is wielding a wand-style vibrator. I did feel a little apprehension at that point, but it was overwhelmed by my urgent need for sexual satisfaction.

Anna stands behind me, the strap-on poking between my legs, rubbing against the soaking material of my panties. Her hands are around me, squeezing and massaging my bound breasts. He must have got on the stage at some point, as the extreme close-ups of my face, my nipples, and my groin attest. My journey from arousal to climax was given a kick-start as Charlotte moved in and jammed the vibrator against my panties, directly over my eager little bud.

As the sequence of pictures show the flush of orgasmic ecstasy suffusing my face, I cum again in the here and now, playing the video of that moment in my head like a corny porn film – me crying out in desperate, glorious release, the audience baying, the incessant machine-gun fire of the shutter, the lightning strike of the flash exploding over and over…

My shoulders slump as the energy of my arousal washes away, leaving only an emptiness. Wearily, I close the computer, creep upstairs, and slide into bed. Feeling the usual post-orgasmic let-down, I reach out and put my arm around my sleeping partner. With a snuffling yawn, he turns and, moments later, we are spooning, and I smile to myself, safe in his embrace.

For now, I have satisfied my base urge. I wonder how long I can suppress it this time? Months? Weeks? Tomorrow? It will be back. It is part of me. Maybe I can share it with my loved one. Maybe. Maybe next time…