Micky watched her sister's arse wiggle as she trotted ahead. Micky had to admit Aggy made a much better pony than herself. But then Mistress had ensured that with a much more rigorous training regime than the one she had put Micky through.

Aggy was eight months into her year-long contract, and Micky was pretty certain Aggy was going to ask Mistress if she could remain collared before the year was up.

Initially, Aggy had shown no aptitude for a life of submission as a slave. Although she had volunteered Aggy kept repeating mistakes. This was not smart-arsed masochism though and so the discipline Mistress metered out was hard for her to take.

The change came after Aggy tried to break out of her pony role with a long introverted rant through her bit. Mistress became incandescent with rage that, once again, the girl had forgotten her place. But despite her anger, she did not beat Aggy. Rather, she kept Aggy in harness for two months. Two months as a pony, twenty-four seven. Two months not speaking. Two months sleeping in bondage, in a stable, on straw. Nine weeks pulling carts, being whipped, washed and fed like an animal.

The woman that emerged was changed. She performed her duties with vigour. Tried hard to please her owner. But she was a quieter soul too. Less impetuous and much, much more submissive.

Micky, when alone with her sister, had quizzed her on the change. Aggy had admitted to an epiphany early on through her sentence as a pony.

She had become convinced Mistress would break her word. That when the year was up Aggy would not be released. Instead, she was going to spend the rest of her life as a pony. After thrashing around in her bondage for a while one night she had fallen asleep certain that she would know nothing but bondage from that day on. The next morning, Micky had come down to prep her for the day. The morning wash, the enema and the supervised toilet. Eating out of a trough before being tacked up and then being tethered on display where the current clients could all see her.

Micky had been so gentle in her care. So soothing and affectionate as she washed and ministered to Aggy's needs. Aggy had realised she was really happy and enjoying Micky's attention. Then it had all clicked into place. All the instructions Mistress had given, the explanations of why a thing was done a certain way. Why slack was not given on some things but was on others. It all just clicked.

Up until then, Aggy had been telling herself that the reason she kept getting it wrong was she was a dominant trying to play at being a submissive. She now realised she was sub, but she had simply been fighting the rules Mistress imposed. As soon as she stopped resisting it all worked.

Micky had pressed her on what that meant with regards her future as a trainee dominatrix. Aggy had just smiled enigmatically and kissed her sister.

That had been another change. Aggy had become a much better lover. That Aggy, Micky's elder sister, was now Micky's occasional lover was a twist she had never anticipated when she had accepted Mistress's collar.

Early on Mistress had commanded them to fuck each other almost daily. Sometimes joining in with the incestuous lovers, sometimes simply content to watch, other times instructing the actions of the girls. Aggy had always obeyed but there had been a stiffness to her actions. The new Aggy was passionate, enthusiastic and a pleasurable fuck. The old Aggy had been a chore, the new Aggy was a treat.

The clincher in Micky's assessment that her sister was going to ask to remain collared though was the tattoos. Mistress had wasted almost no time in altering Aggy's appearance to match her younger sister. Her hair was cut to match straight away and the piercings were installed in quick time too.

But while Mistress continued to work on Micky's sleeve, no ink was applied to her sister. It made sense. One day the collar was coming off, and while piercings could easily be removed, tattoos were much harder to shift.

Shortly after her long stint as a pony, Aggy had timorously enquired why Mistress had not yet tattooed her. As if the reason was not obvious. Mistress, not one for mind games and a big fan of plain speaking had told the girl, "she damn well knew why," and then asked, "So why are you asking?"

Aggy had confessed to being jealous of her sister's ink, and what it stood for. Mistress had rewarded Aggy with a BDSM triskelion to match Micky's, then a kitsch "slave" just like Micky's and finally a photo-real portrait of Aggy as a pony was inked onto her forearm.

Micky knew the forearm and crotch tattoos would be easy for her to hide from future clients. But that she had begged her Mistress to mark her permanently, just like her sister slave, suggested Aggy had reassessed her life goals.

The big shift for Micky was realising she too wanted her sister to remain collared. The jealousy that had initially burned within had melted away. Her love for her sister had never been stronger. Though strangely it was not the regular sex with her sibling that had bolstered her affection. Rather the camaraderie.

Watching her sister make many of the same mistakes she had made, and suffer the same embarrassments, had made her sister more endearing. Aggy's dismay at having to greet the grocery delivery man dressed in a latex french maids uniform was priceless. Only to be eclipsed when he demanded a blow job, like her sister handed out, when there were no substitutions.

Seeing her sister struggle in ballet boots or being there to massage each other's feet, shoulders, arms or legs after a heavy session. It all meant that they suddenly related to each other in a way they never had before. As children, they had competed. Sibling rivalry warred with their parents' instruction that they should love their sister.

As Samantha's slaves, they got what they were given. There was no need to compete. There was more than enough love to go around and so Micky found she really did love her sister.

Arriving back at the stables Micky had methodically stripped her sister from her tack. The task was done silently for the most part as Aggy took some time to stop being a pony. Once the boots were removed and the bridle was cleaned and hung up though Aggy came back and let out a melancholy sigh.

"You okay, sis?" Inquired Micky.

"Oh, yeah, I'm alright... It's just... On nice days like today. After a nice trot like that. Sometimes I wonder if I have the courage... Oh... It's..."

Micky raised her eyebrows at her incoherent sister as if to say, "Spit it out already!"

"Damn, Micky! Sometimes I just wish Mistress kept me as a pony all the time is all."

"Really? Oh! I hope not. I've just found you. Learnt to love you. If you were a pony we'd never talk. I enjoy exercising you and grooming you and all... But I much prefer you as a sister slave than a dumb animal."

"I know, I like being a slave too. It's just being a pony is just so fulfilling. I just feel so content when I'm in harness."

"Well you are not in harness now, but you are locked in a collar. Which means, slave, that you and I have to report to the dungeon. Apparently, Mistress is lending us to some American client to play with."

"Since when do clients play with us? I thought the odd one got a blow if they were good."

"If you'd not spent all that time in the stable you'd know Mistress has been chatting to some illustrator from Florida."

"Well, it's moot where he's from, sister, we'd better get in hadn't we?"

oOo

They arrived in the dungeon to find only Mistress waiting for them. If there was a client about he had yet to appear. Mistress though had been busy, as the flogging bench had been moved to the centre of the floor space and ankle stocks set up at either end. Additionally, a short steel pole had been installed in the middle. At the top of the pole sat a padded cross piece. Protruding from that was the head of a wand vibrator, with two dildo's either side and two butt plugs on the outside. It was immediately clear where the two sister slaves were to go.

"Climb aboard girls," beamed their owner, "face to face, if it's not obvious. I promise you this one is going to have you in stitches. Mikaela, remove your uniform first, pet."

Micky stripped and the two women climbed up onto the padded bench. Aggy lowered herself upon the horned saddle first her face lighting up as the two phalli entered her body. Micky dutifully followed suit discovering the reason for her sister's pleasure, the vibe was already on and running on a slow setting.

The two slaves knelt face to face pressed up against each other smiling at their predicament. If only all of Mistresses bondage scenarios were so comfortable.

Mistress then took each of the girl's ankles and placed them in the stocks behind them. Thus trapping them in place and forcing them to lean harder into each other. Not content with that the dominatrix cuffed each slave's wrists behind their sister and then attached them to the back of their partner's collar. Samantha then pushed the girls apart temporarily, to link their nipple rings, and then pushed them together again to connect their collars.

Micky was used to being in such close proximity to her sister. In fact, she enjoyed it and this was proving no exception. Aroused by the bondage, the vibrator and the dildos, as well as the heat of her sister she kissed her sibling deeply as their owner compleated restraining them.

Mistress was doing something to her toes. An experimental wiggle confirmed they had been tied to the back of the stocks that secured her ankles. Why on earth?

"Comfey, girls?" Inquired their owner.

"Yes, Mistress," they both answered in unison.

"Good, silence from now on though, slaves. I'll explain why in a minute." Their owner then wrapped extra slim leather collars around their throats, just above their regular steel ones. After that, she used three broad leather straps or belts to crush the sister's torso's into each other. With the buckles at their sides, the girls could not reach them. Micky now felt her sisters every breath. They were squeezed so tight they now rested their chins on their sister's shoulders.

"The straps squeezing you so tightly together are to stop you injuring each other. I've also put throat mics on you. If you utter any sound you will shock your sister through those lovely dildo's your sitting on. So if you can, may I suggest you keep very quiet from now on. I'll go fetch our guest now. Remember, no talking."

Micky watched her Mistress stalk off. The dildoes would shock her? This was very elaborate for Mistress. Samantha was a strict, and often sadistic, Mistress. But predicament bondage was not her usual MO. Perhaps this had been requested by the guest.

Mistress returned, escorting a man. He was better built than most of the regulars, dressed in a well-tailored suit. A thick beard that matched his salt and pepper hair was surrounding a well-tanned face. This gentleman had seen some sun or lived under a sunbed.

"Are they twins," he asked in a clearly American accent after the pair had circled the bound slaves.

"No, the elder is senior by eleven months. But their parents clearly only had one mix of DNA as the pair are almost identical."

"How long have you owned them?"

"As a pair, only eight months. The youngest I acquired first. Her sister is here, ostensibly, as an apprentice dominatrix. However, she is presently trying to muster the courage to ask me to make her collar as permanent as her sisters. This would be the smart move. She, like her sister, is a born slave. She craves to be a ponygirl. If she asks promptly I'm inclined to grant her, her wish."

"You keep them in bondage all the time?"

"We don't role play here. Mikaela and Agnetha are slaves twenty-four seven. Mikaela is already committed for life. I will never free her. Agnetha will follow suit. Both of these slaves will live out their lives in collars."

"Wow! I must say they are an impressive pair. You must be delighted to own them."

"I'll be honest with you, sir. I consider myself lucky beyond my wildest dreams. A matched pair of submissive sisters. It's the stuff of fiction, isn't it? I will cherish these two forever. Happy does not cover it. Which brings me to the terms of our agreement. Any of the tools here are yours to use and enjoy. As are the slaves. However, may I insist that your own personal trouser snake enters their mouths only. Finally, no permanent marks, please. As I said, they are my most cherished and loved possessions."

"Ma'am I consider it an honour that you have allowed me this access..."

"Good, well I'll leave you to play," she turned to the slaves, "This man is your Master for the duration, girls. Obey him. When he dismisses you I want you both in uniform and upstairs straight away. Now all of you play nice and have fun."

oOo

Micky screamed with laughter. She no longer cared that her sister was being shocked. She'd received enough of her own. The man was an evil genius. It was incomprehensible that she was still finding herself laughing. Squashed as she was her sides were in agony. She had wet herself and she was sure Aggy had too. Her feet were sore from the crop and her backside was glowing from the paddle, and yet he kept tickling.

Both Micky and Aggy thrashed in their bondage. Temporarily oblivious to their sister's distress as the Master of their torment played with their nerves. Pinwheels, floggers, feathers and even his fingers. He just kept pushing them harder and beyond. If Micky had ever wished for a safe word before it was now. The man was diabolically good.

Eventually, they were released from the bench. Though not from each other. So that it was on their knees, still squashed together they slobbered and sucked on his manhood.

When he came it was deep in Micky's throat as her sister sucked on his balls. Satiated the man stood up and put himself away. He then gently separated the two slaves smiling as he did so.

The girls released, the man departed. Micky stared at the man's retreating back, realising he had uttered not one word at them.

"He was amazing," Aggy broke the silence.

"As was that setup," agreed Micky, "Do you think Mistress will do that to us again?"

"God, I hope so," sighed Aggy wistfully. The look on her sister's face reminded her of their owner's words to the client.

"So, sister, you going to pluck up the courage to ask now you know Mistress is waiting?"

Aggy did not respond immediately. She stared at Micky with her eyes wide and her lips pressed together in excitement. Then she nodded.