"Harriet, left a bit," my Master shouted, indicating from the other bank with an expansive wave of his hand that I should move down river. I followed his gesticulating arm and trod further down. Almost instantly I saw the ball, nestling in the middle of a clump of vivid green nettles.

"Oh shit," I shouted. Gingerly, I pushed my leg forward and hooked my foot backwards, trying to drag the ball with the sole of my trainer. The nettles gravitated towards my bared ankle, strafing my flesh with their barbed, poisonous leaves and causing me to wince with pain. The ball moved an inch towards me, before settling once more into its easy refuge. I tried again, less tentative and more desparate, and once more my ankle felt the rash of pain as the nettles grazed against them ruthlessly. This time, the ball slid further and, readjusting my position, I got my whole foot on top of it, dragging it forcefully towards me. Triumphantly, I bent to pick it up.

It was sodden and bedraggled, well chewed by the stranger's dog, with tufts of matted felt protruding from it amid a number of completely bald areas. It looked disgusting and I balked at the idea of putting it in my mouth. My Master had given me my instructions, however, and I knew that if I failed to obey them in full he would regard my endeavour as a complete failure. And I shuddered to think what the price of such failure might be.

Reluctantly, I lifted the ball to my mouth and tried to get a grip. It was far too big and I couldn't fit it in. I pressed and pushed, but to no avail, and finally I gripped a large tuft of stringy felt between my teeth. Shaking my head from side to side to test how firmly I could hold it, I stepped from the shrubbery back onto the riverside path.

Where I stood face to face with the couple who had been walking towards me.

I stopped on the spot, frozen by surprise and instantly embarrassed beyond comprehension. The couple stared at me in amazement, their eyes running up and down my naked body a few times before finally focussing on the hideous tennis ball hanging from my lips. Eventually, I found the will to move, waved ineffectively at them and sped up the path as fast as I could, ridiculously clenching my buttocks for fear that my wobbling backside would appear too large to my unbidden observers.

My exposure heightened my emotions considerably, and my heart was hammering in my chest, not simply through exertion. I couldn't begin to think what the stunned couple would have thought as they saw me emerging naked from the undergrowth, a dog's ball lodged in my mouth. The shame of the experience filled my head, overloading my senses and leaving me breathless. I reached the bridge and sprinted over it to the other bank, the whoosh of the wind on my bare skin adding to my discomfort. Purposely not looking to my right, to avoid seeing the couple again, I sped towards my Master and the stranger. As I neared them, I again became self-conscious about my body, about my small tits jiggling aimlessly with each step, about the flesh of my thighs rippling, about my face, red with fatigue and humiliation. And most of all, about the ridiculous ball which was wobbling in front of me. My grip on the tangled threads was loosening, and the impact of each footstep dislodged it still further. Despite my impatience to be back in the security of the picnic area, I had to slow to virtually a walking pace in order to keep it firmly in my mouth.

My Master and the stranger stood watching my arrival with, I thought, looks which mingled amusement and admiration. Exhausted, I launched myself onto the blanket, dropped the ball at my Master's feet and fell to my hands and knees in front of him. Too late I realised how this must look.

"Well done, girl," my Master said patronisingly, patting me on the head as though I were a dog. He reached down and tickled my chin. A wave of humiliation flooded over me as I realised what he was doing. "Did you enjoy that?"

Too exhausted to speak, I nodded.

"Good. Most little doggies like to do that over and over again, so here we are. Fetch, Harriet."

And with that, my Master threw the tennis ball once again. This time, however, he didn't throw it as hard and the ball landed in the middle of the river. Appalled, I looked at it as it started to bob downstream, being carried along by the gentle current.

"You can't be serious?" I breathed.

"Deadly. Fetch, girl."

My legs felt like lead as I dragged myself to my feet. Trembling, I looked at him imploringly, but he was resolute and I knew there was nothing I could do. Once more I set off in chase of a dog's ball. Gingerly, I eased myself down the banking to the edge of the river and tentatively stretched my foot out. The water was freezing and I shrieked. Looking back, I saw my Master observing me sternly, his eyes commanding me to continue. I stepped forward, sinking to my ankle in the ice-cold water and then dragged my left leg through the flowing stream, establishing a shaky, shambling progress towards the centre. The water was rising with each step, and soon I was up to my knees.

The ball was bobbing downstream, caught up in the eddying current, and the faster I moved towards it the faster it seemed to pull away. I was struggling to make any headway, chasing it downstream, all pretence at subtlety gone as I crashed and splashed through the water. I was completely soaked, the chilling water gripping numbingly at my skin. And still I couldn't reach it. I lunged forward and lost my footing, ending up sprawled on the river bed, my bum resting painfully on the scratchy stone surface.

From behind I heard a splash and turned to see the stranger's black labrador lunge into the stream. With a grace and ease in direct contrast to my lumbering effort, it bounded downstream in search of its ball and within seconds had retrieved it. Eying me with, I fancied, a triumphant look, it headed back to the bank and morosely I followed suit, bedraggled and miserable.

By the time I reached the blanket the dog was already standing happily beside the stranger, the ball at her feet. Wearily, I dragged myself on to it and lay once more on my hands and knees beside my Master, breathless and shivering. I felt that I had failed him. I felt that I had lost the game to the labrador, and I sat silently beside him. The final ignominy came when the labrador shook himself vigorously, covering me with a shower of water from his sleek, gleaming coat.

We sat, the labrador and I, at the feet of our owners and looked up at them obediently.