After perhaps an hour of this public exposure, my Master sat up and stroked my back to attract my attention. I turned round and pulled myself up.

"Harriet, I want you to go down to the water now and have a brief swim."

"Yes, Master," I said cautiously. I was no great swimmer, and the thought of swimming in the North Sea somewhat alarmed me.

"You don't have to go far. I want you to go into the water until you are completely covered, and swim around for a few minutes. Then you can come back."

I was relieved. This didn't sound too difficult. I had expected something worse, something rather more demanding. It was clear that my Master was intending today to be a test for me, and I expected things to get progressively more difficult, from the simple flashing on the journey to... To what? There must be more, I thought.

And there was.

"While you are walking down and coming back, I want you to select which person you want to have sex with you today."

I said nothing. What was there to say?

"Male or female, it's up to you. Attractive or ugly: you choose. Young or old: I don't care. A single person or a couple, or even a group if you wish. It's all up to you, but make your choice. It will be your task for the rest of the day to find a way of allowing them to have you. You will have to chat them up and seduce them, lead them on and turn them on, and then find somewhere where they can have you. Is that clear?"

I nodded, dumbstruck.

"You can go now."

Jesus. What next? Pick up a stranger on a beach and fuck him (or her). I was accustomed to my Master finding new ways of tormenting me, but this was one I had not expected. Picking myself up from the blanket, I slowly made my way through the throng of bathers, acutely conscious of the effect my virtually naked body was having as I sashayed past their prone bodies. Heads turned, people nudged one another, comments were made; my procession to the beach was anything but an unobtrusive one. All the while, of course, I was scanning them for a likely candidate, searching for the lucky soul who, unknown to them at this stage, was going to become considerably more intimate with my body before the end of the day.

It wasn't promising, though. I had pretty much settled on choosing a single person. A group would have been easy to chat up, but difficult to fuck without half of Hunstanton seeing, and a couple would have been fun, but hard to chat up. I was left, then, with the task of finding a single person, but there were precious few of them, and those there were belonged to the Johnny-no-friends school, all buck-teeth, cross eyes and alarming twitches. I began to despair as I reached the water's edge. I had only seen a couple of even vaguely promising possibilities.

I deliberately ignored anyone who either tried to make eye contact or speak to me, on the basis, as my mother always used to say, that "want doesn't get." Of course, she never met my Master, who would have disabused her of that foolish notion. But I didn't want anyone pushy, so I ignored them. Likewise, I walked past couples who were obviously wrapped up in each other and singles who had withdrawn into themselves. Maybe I was being too picky, but it appeared that in the whole beach there was nobody suitable.

I splashed about in the gently lapping water for a while, pretending that I was accustoming myself to the cold before preparing to launch into it, but in reality allowing myself a while longer to peruse the available talent. After a couple of minutes I had narrowed the choice down to two: a single man who was reading The White Hotel, and would therefore, I concluded, not by averse to some unexpected sexual advances, and a woman who, in defiance of the fierce sun, had a perfect, alabaster-pale complexion and a dreamy moon face.

Having narrowed down my options, I turned and prepared myself for the next ordeal, the water. I knew there was no point in shilly-shallying on the edge, and instead galvanised myself and, with a scream, lunged full-tilt into the water; I pressed on until it was above my knees, by which time the drag of the water slowed me almost to a halt, and I launched myself head first onto the oncoming waves. Immediately, the heart-stopping cold of the water sent me reeling, knocking the air out of my lungs, tensing every muscle and ripping through every nerve ending. It was awesome: terrifying, painful, sense-heightening, excruciating and thrilling all at once, just like good sex; indeed, such were the sensations piling through my body that it did feel exactly like a climax. I was aware that I was screaming and thrashing in the water, and I must have looked like a Jaws victim, but after a few seconds I composed myself and, steadying my body, began to float contentedly in the water.

As my Master had commanded, I spent a few minutes in the sea, my body gradually acclimatising itself to the extreme cold, so that it no longer felt unpleasant but, rather, invigorating. I bobbed about in the waves, feeling their formidable, dense power thrum against me, and contemplating my next move. I would have to make my final selection before I returned to my Master, have to choose whether I wanted The White Hotel man or the alabaster woman. Well, I thought, if 'twere done, 'twere as well done quickly, and I headed back towards the beach. A few yards from the water's edge, my feet hit the bottom, and I began to pull myself upright in the water.

And my white bikini was completely, totally transparent.