"What's the matter? Doesn't the slave girl want to do that?" she enquired tartly. I shook my head silently. "Too bad," she cried. "You said it, girl, you said you'd do anything. So get on with it."

Kathy looked as though she were about to intercede, but Siobhan gave her an implacable look, her arms folded, clearly in no mood to compromise. Kathy backed down and remained silent. I was on my own.

"So?" Siobhan said, arching her eyebrow.

Slowly, I made my way towards her chair and knelt before it. She didn't move, but sat staring at me. Confused, I looked back.

"Ask," she said.

"Oh, come on," interjected Kathy.

"No, I won't come on," Siobhan replied. "If she wants to do this, she can do it properly. And proper slaves grovel. So ask, Harriet."

I sat on my haunches, staring at Siobhan. Well, I thought, I may have underestimated her. There seemed to be a certain steel there, a resolve which I hadn't recognised before; perhaps she had picked up some assertiveness in the years since we last met. I could feel my cheeks flush as I contemplated my situation. I had manoeuvred myself into this one, and didn't deserve any sympathy or understanding, which was just as well, because it seemed unlikely that Siobhan would show any.

"Please," I asked, staring into her eyes, "please let me kiss you."

"Kiss me where?"

"Your arse."

"Ask properly."

"Please let me kiss your arse."

"My bare arse?"

"Yes, please. Please let me kiss your bare arse." My God, I thought, this was happening; she was going to go through with this. I sat before her, fascinated, excited and appalled in equal measure by the prospect which faced me. This was my best friend.

"Very well," she said. "You can take off my trousers." I gulped and rose towards her. Deftly I undid the button and was about to pull down the zip when she interrupted. "The zip with your teeth."

I stared at her with blank amazement: she really was doing this, really was getting into it. Cheeks flushing even more, I lowered my head to her crotch and fiddled with the zip until it caught between my teeth. I tugged at it a couple of times; at first it snagged and wouldn't budge, but by pulling it up and then down again I managed to release it and undid it completely. Siobhan said nothing, but raised herself off the chair, allowing me room to pull her trousers from her. I did so, drawing them to her knees; she assumed her seated position again, and I tugged her trousers free from her legs and over her feet. Siobhan sat before me in white, cotton panties.

"So then, slave girl, still enjoying this?" she asked. What a question. And the answer? An outright no and a categorical yes. There can never be any middle ground; ambivalence has no place in the world of dominance and submission. Doubt, however, has a strong role to play, the uncertainty, the confusion, the blurred space between pleasure and pain, humiliation and desire. And which did I feel? All of them, all of them. I made no gesture to Siobhan, but sat still, awaiting her order.

"Kiss my knee, Harriet." I did so. Lowering my mouth to her and planting my lips on her left leg, I gave her a lingering kiss. "Very nice," she said. "Keep kissing. And move slowly - slowly - up my leg." Again, I did as instructed, and began to plant kisses, one on the other, up her leg, until I reached her upper thigh. "Stop!" she cried.

I halted immediately and rocked back onto my heels.

"Mmm, very nice indeed," she said. "You have a nice technique, girl." Saying that, she turned onto her side. "Now, continue." I resumed where I had left off, kissing her thigh, but it was clear from her position that she now expected me to move round to her back. Accordingly, I began to drift over her thigh, my tongue tracing a slow, deliberate route over her pale, fresh skin. Finally, I was kissing the back of her legs, just below her panties, long, delicate kisses, one after the other. My face slid down her thigh, and my mouth fell into the vee between her legs, feeling the heat from her body, tasting the slight sheen of sweat on her skin, my nose nestled against the fabric of her panties.

"Very good, very good," Siobhan murmured. She pulled herself up slightly in the chair, pushing her rear up and outwards at me; her shapely buttocks pressed tightly against her panties, forming two beautiful spheroids. It was clear what Siobhan wanted. I inhaled deeply and lifted my head towards her. Puckering my lips, I pressed them lightly against her panties, planting a lingering kiss on her right cheek. Well, Harriet, I thought, you're doing it: kissing your best friend's arse. I continued to ply kisses on her rear, crossing one cheek and then the other. Siobhan was sighing heavily, and I realised that she was getting turned on. Lifting my head from her arse, I sat back for a moment, and there, indeed, was a slight damp patch on her panties: she was wet; I had made her wet. A tremor of excitement rushed through me at that revelation, the realisation that I had managed to arouse Siobhan giving me immense satisfaction.

"Oh, Harriet," she sighed, "that is quite delightful. Take my panties off now, I want to feel your tongue on my bare arse."

Although I had known this was what was going to happen, the bald instruction left me somewhat shocked for an instant. Quickly, though, I composed myself and raised my hands to her panties. Gripping them, I gently tugged them down and over the beautiful arse I had just been kissing, revealing its splendour to my gaze. She was stunning, magnificently curved, her cheeks firm, her skin silky smooth. Hastily, I slid the panties down her legs, pulled them off and sat before her, staring, drinking in her beauty.

And then I kissed her. Slowly, I lowered my head to her and placed my mouth on her upraised cheek. The feel of her skin, soft and pearly, was heavenly. I planted kiss upon kiss on her, covering first one cheek and then the other, dragging my tongue over her, licking and kissing, licking and kissing. Siobhan buried her head in the chair, pushing her arse further into the air, and then further yet, so that her cheeks parted and a dark, glistening vee emerged between them.

I knew where she wanted me to go.

Starting at the top of her bum, I began to lick downwards, tracing a path down the crevice. Her excitement showed in the muskiness I could smell as I kissed and licked downwards and downwards. Siobhan moaned loudly, and I took stock of my situation. My head was buried in my friends backside, licking and kissing downwards inexorably until...

Until I came to her hole... And I kissed it, I kissed her arsehole, ran my tongue round and round it. It tasted heavenly. Siobhan was moaning continuously now, and making no attempt to conceal her excitement. I pressed my tongue against her, pushing hard, and felt the very tip penetrate her hole. I realised that she had her hand at her pussy and was rubbing herself furiously. Gripping her cheeks, one in each hand, I pushed at them, prising them apart, and redoubled my efforts with my tongue. It slid further inside her, and as I released her cheeks from my hands I felt her muscles grip it. Continually pulling at her cheeks and pressing with my tongue, I managed to ease it some distance inside her, and did my best to manoeuvre it, feeling it press against the sides of her arsehole. Siobhan let out a shriek, and then another, and her thighs tensed. Her sphincter muscles contracted involuntarily a few times, gripping and releasing themselves on my trapped tongue, and I made my final assault, pressing as hard as I could against her; my face was now lodged hard between her cheeks, my tongue wormed right up inside her. She howled and I felt her orgasm rush through her, causing her legs to shiver and shake, moment after moment, wave after wave. Gradually, I felt her excitement subside and I freed myself from her arse. I planted one final, delicate kiss on her flushed cheek and sat back.

"Was that okay?" I asked.