Part 1

"Well what do you think?" Kate asked as she led Nicole and Dania into the cellar. The women looked at the heavy metal box that was no larger than 1.5 foot cubed. "Well how do you restrain someone in that?" Nicole asked disappointedly. "Oh easily" Kate smiled.

The box was made up of two halves with a join around the middle allowing the top half to lift up. It had a round hole in the middle of one side that was half in each part of the box. It also had a glass like surface on top.

"Its made of two inch thick hardened steel" Kate explained. "It's bolted to the floor although its so heavy it can't be moved anyway. Why don't you try it first" she smiled to Nicole as she took a key out of her pocket. She turned the key in the keyhole and the box opened on its hinges. "Just put your head in here" she purred to Nicole as she tapped the box with her heel.

Still wearing her summer top and skirt from the beach, Nicole knelt down and slowly put her head inside the box, with her neck resting in the bottom half of the hole. Kate, also dressed from the beach in a light thigh-length skirt and top, sat down on to the box and smiled as it gently closed under her weight. As it closed completely there was a small click. Kate then reached down and removed the key and dropped it into her cleavage.

The hole in the side of the box had closed securely around Nicole's neck so that her head was now trapped inside the box. Inside the box was padded and comfortable but quite tight with only a couple of inches space around Nicole's head. It was also dark, with only a small amount of light coming through a heavily barred grill "That's how you restrain someone" Kate smiled, "I hope you find it secure enough".

"Although maybe I should also tell you about the extra security feature" she continued as she pulled her skirt out from underneath her and stretched her legs out in front. "The top of this box is fitted with a highly sensitive pressure meter which right now is sensing my bum sitting on top of it. If I press this button here, the sensor will scan and remember the exact shape and weight of my bum."

Kate pushed the button and watched as the green light started flashing and then after about ten seconds turned to red. "That's it, the box is now double-locked" she smiled as she retrieved the key and tried in vain to turn it in the lock. "Now this is the nice bit, the only way to release the double lock is for the sensor to sense my arse again and until it does that, the box will stay locked and your head, my darling Nicole, will stay imprisoned inside."

Nicole heard Kate's explanation through the small grill that allowed air into the box and started to try and pull her head out. Kate sat down on one of the stools and smiled as she watched Nicole's efforts. "I'm about the same size as you" Dania said to Kate, "give me the key and I'll try to open it". Dania sat down on the box and like Kate, pulled her skirt out from underneath her. She pressed the red button and waited. After a few seconds the red light flashed. "Looks at though my arse is pretty unique". Kate smiled.

Guessing that Kate was a little lighter than her, Dania took some of her weight on her arms and again pressed the button. When that failed, she pushed down a little harder with her thighs to try and replicate Kate's strong legs. Dania finally turned to Kate and said "Turn around and show me your butt". Kate laughed, "When a prisoner is trying to escape from prison she doesn't get to see the shape of the key". Dania smiled, "I know, but without a quick peek Nic's chances of escape don't look good!"

Kate did as she was told and lifted her skirt. Dania came over knelt down and ran her hands around Kate's hips. "Are you sure you are close enough" Kate asked as she reached behind her and pushed Dania's face into her black silk knickers. "The shape is now imprinted on your face" Kate smiled as Dania returned to the box and continued to position her bum so as to match Kate's.

"I give up," Dania finally conceded. "See I have a unique bum" Kate smiled as she walked over and sat down on top of Nicole's head. She pressed the button and within a few seconds the light turned green. "That's amazing" Dania replied as she inserted the key in the lock and finally opened the heavy steel box.

Nicole climbed to her feet and looked across to Kate, "It is definitely your turn" she purred. "No way" Kate replied, "this is just too scary and secure". With that, Nicole took Kate by the hand and forcefully pulled her over to the box. She held Kate's head in place and smiled, "OK Dannie, show me how this works". Dania slowly sat down on top, closing the box with Kate's head inside. When it finally closed the locked clicked and Kate fate was sealed. "I think I'll hold the key," Nicole purred.

Dania then pressed the green button and waited while the force she was exerting on the box was analyzed. The light then turned red, "Try and break that code, Katie" Dania smiled as realising the time, she ran upstairs to change.

When Dania returned, Nicole was sitting on the box, but had given up trying to break the combination set by Dania's arse. "I have to go out now" Dania smiled, "and I'm just wondering whether I should let you out before I go" she teased Kate. "Please" Kate replied from inside the box, "please!"

Now wearing her jeans Dania sat down on the box and pressed the button, however the light stayed red. "Don't know how to tell you this Katie, but not even my butt can get you out this time!" "Are you wearing the same clothes?" Kate asked. "Good point, those jeans are quite tight, they probably change the shape of your butt" Nicole observed.

Dania slipped out of her jeans and again sat down on top of Kate's head and again the light stayed red. Dania was starting to get worried, although Nicole was starting to smile. "Haven't you changed your panties?" Nicole asked, "those white ones you were wearing before had a word embroidered across the back. While Dania continued to try to unlock the box, Nicole ran upstairs and found Dania's knickers.

"Katie, these may be your only hope of freedom" Nicole smiled as she held up Dania's used panties. Dania took off her new knickers and put the old pair back on. "I think they were riding up my butt a bit," Dania said as she adjusted them on her backside. Dania sat down above Kate's head again and pressed the button. "Your lucky day" she purred to Kate as she watched the light turn green.

Dania jumped up and changed back into her jeans. "Have fun girls" she smiled as she blew Nicole a kiss. Once Dania had left, Nicole went over to the box, pulled down her knickers and pulled up her skirt and sat down so that her bare bum was resting on the box. "I'm totally naked on top of you" the blonde smiled as she pressed the button and the green light turned back to red.

Nicole pulled up her panties and knelt down by where Kate's head disappeared into the steel box. "At least you know what my arse looks like, so you should be able to describe it to any rescuer" she smiled. Nicole then ran her fingers down Kate's body to her skirt. She lifted her skirt to reveal Kate's black knickers. "And to think that when I was incarcerated just now that your little butt was the only thing in the world that could free me" she purred, "and now my naked bum is the only thing that can give you back your freedom".

Nicole bent over and kissed Kate's knickers. She then turned Kate over so that she was on her side. She lifted Kate's top leg and put her own head between Kate's thighs. She then pulled Kate's leg down on top of her enclosing her inside. Kate soon complied with Nicole's wishes and tensed her legs tightly around Nicole's neck.

Nicole finally grew tired of playing and stood up. "I suppose you'd like me to sit my naked butt back down on your head?" Nicole smiled as she did just that. The box remembered Nicole's butt and duly opened. Nicole turned the key in the lock and opened the box.

"About time!" Kate exclaimed as she climbed to her feet. "What was the rush?" Nicole purred back. "My dinner appointment!" Kate replied. "OK, but before you go can you just sit down for a moment?" Nicole asked. Kate turned around and saw Nicole's head already positioned in the box.

"Look I'll be out until the early hours," Kate explained. "Please Katie!" Nicole begged. Without replying, Kate lifted her skirt and sat down closing the box beneath her. It clicked shut and she removed the key from its hole. She wriggled her arse until she was sitting nicely on the lid and then pressed the button and watched the light change to red.

"One day I might decide to keep you as a permanent sex slave" Kate purred as she ran her bare feet along Nicole's toned body". Kate stood up and smoothed her skirt back down. "Maybe I should also make you wait for your fun until I return" Kate smiled as she picked up two sets of handcuffs and taking each of Nicole's hands in turn locked them to metal rings welded on to the box. Nicole's hands were now secured up by her head and far away from her knickers.

Kate took the handcuff keys and tucked them inside Nicole's panties. "So near and yet so far" she joked as kissed Nicole on the bum. "And don't even try to escape from the box" Kate smiled as she tapped herself on the arse, "there really is only one key to release you!"


Part 2

It was 2 o'clock in the morning when Kate returned. She walked in and found Nicole exactly where she had left her with her head still securely locked in the box. Nicole was fast asleep despite her restraints.

Kate pulled the key from her handbag and turned it in the lock on the side of the box, but the box remained firmly locked with Nicole's head inside. Kate sat down on top of the box, pulling her skirt out from under her so that only her knickers were resting on the sensor. She pressed the button and the sensor analyzed her butt to check that it was the same one that had locked the box. The pressure that Kate's but exerted on the sensor was the correct weight and shape and the electronic lock was released.

Kate lifted the lid of the box to reveal Nicole head inside. The blonde was fast asleep, "Wake up sleepy" Kate called.

Nicole stirred slowly, "What time is it?" she asked.

"Two in the morning" Kate replied as she unlocked the cuffs she had secured around Nicole's wrists. "Come on, I won't hold this heavy lid open for you all night, Nic, get out now or be locked in until the morning."

Seeing Nicole close her eyes, Kate lowered the lid back down. She reached under her skirt and pulled off her knickers before sitting back down on the lid. She felt her naked butt against the hard lid and wriggled around a little until she was ready to be scanned. She pressed the button and imagined what the sensor would be making of her butt and how it would be translating it into a digital code that only her butt could replicate. The light turned red, "That it for you" Kate smiled, "my butt is now off duty!" Kate went to bed leaving the key still in the lock, without her butt the key was useless.

Kate woke just before midday and finally released her friend. Nicole showered and walked back into the room in short gym shorts and t-shirt. "I want to try something out on you" the blonde smiled. "I want to see if my daily cycling and step workout really does improve my butt and this box is a great way to find out. And just to add interest to the experiment, I want your head locked inside at the time."

Kate was reluctant but having herself incarcerated Nicole in the device for the last twelve hours was not in a position to refuse. She lay on the floor and put her head inside the box before Nicole lowered the lid into place. The box was a tight fit around the brunette's neck and Nicole smiled as she watched Kate try to pull her head out of the closed device.

"I'm now sitting on the lid and the sensor is analyzing my unexercised butt in my gym shorts" Nicole explained to her co-researcher as she watched the light turn red and the box lock. "Now we'll find out whether my workout changes the shape of my butt, or should I say the only key to your freedom!"

Nicole started with the exercise bike and then moved to the step machine. With the music blaring she worked for an hour on all her exercises designed to improve her butt. By the time she stopped she was exhausted. She stood in front of the mirror and admired her out arse, "Looks good" she smiled, "let's see what the box thinks!"

The blonde sat back down on the lid exactly as she had down an hour before. She pressed the button to her delight the light stayed red. "Yeah" she exclaimed, "proof that my workout works". She tried a few more times to unlocked the box but with no success.

Kate was getting concerned, "How are you going to let me out!" she said from behind the small grill that was her only connection with the outside work. "You've locked me up in this maximum security box and now changed the shape of the only key!" Kate exclaimed. Nicole knelt down and looked in through the small grill, "Sorry Katie, I really didn't think it'd work," she said as she ran her fingers down Kate's back.

"I'd better take a bath and try and relax my tight little butt muscles," Nicole purred as her fingers made their way down to Kate's legs. "And anyway, while your enforced incarceration for who knows how long is a pity, on the bright side my butt looks fantastic" the blonde giggled.

As Kate lay trapped with her head locked in the heavy metal box, Nicole lay in the bath massaging her legs and butt with her hands. An hour later Nicole returned and lay down with her panty-clad butt against the grill. "What do think?" Nicole purred, "Does that look like the right key to your restraint?"

Kate looked at the blonde's butt, "What do we tell people we were doing this morning, waiting for your butt muscles to relax so that you can release me?" Kate smiled.

"The truth is always good" Nicole giggled as she stood up and sat down on the box. "Cool" Nicole smiled as the light turned green.

The following day Kate and Nicole sat in the café having brunch. "I've got the perfect plan to get you back" Kate smiled as she finished her coffee. "I've chosen an interior designer at random from the phone book and invited her round to give us her ideas". Nicole looked confused but knew that all would become clear.

The girls were back in the house when the interior designer arrived. She was attractive, in her mid-thirties, slim and medium height with long dark hair and wearing black trousers and top. She introduced herself as Rebecca. Kate led her into her bedroom and started talking about how she wanted the room to look. As she was measuring up, Kate led Nicole back to the lounge where she had positioned the box under the large picture windows that looked out to the sea.

"Inside" Kate ordered as Nicole knelt down gingerly and positioned her head in the box. Kate closed the lid and turned the key in the lock. "Now I'll pocket the key to keep you here for now, but when Rebecca returns let's see if we can't get her to offer her cute little cute as the code for your incarceration. Oh and by the way, I've turned off the 24 hours failsafe feature, so if anything goes wrong then..."

Kate positioned a coffee table over Nicole's body and threw a drop sheet over it. She also positioned drop sheets over the other furniture to make the room look as though it was ready to be painted. She then placed a table next to the box and placed a low stool by the table on the other side from the box. "Perfect" she smiled, "The box that your head is in looks just like a seat for Rebecca."

Kate returned with Rebecca to show her some ideas she'd seen in some magazines that she had left on the table. "Take a seat" Kate smiled as she beckoned to the box. Not realising that it contained someone's head, Rebecca sat down on the lid. As she looked at the magazines, Kate pressed the remote trigger. The sensor started to analyze Rebecca's butt, its shape, its size and the force that it exerted on the lid. Once all the information had been collected, the lid locked. Rebecca heard a small click beneath her but Kate easily diverted her attention back to the pictures.

Half an hour later Rebecca left to collect some more samples. Kate walked over to the box and lay down by the grill. "Oh my, Rebecca's butt, the only key to your freedom is now driving back into town" Kate giggled.

"I don't believe you locked the box with her on top" Nicole replied nervously.

"Oh yes I did" Kate smiled, "but to prove it let's see if I can release you". Kate sat on the box and tried to release the lock. "It's certainly not my butt that'll open this" she purred as she lay down by the grill again.

"What was her butt like" Nicole asked.

"Nice" Kate smiled, "Small and toned"

"Do we know anyone else similar?" Nicole asked hopefully.

Kate shook her head, "As far as the sensor in the box is concerned, Rebecca's butt is unique in the world, but don't worry she'll be back this afternoon".

Two hours later Rebecca returned but she was now wearing a short skirt and top. "You've changed" Kate said somewhat taken aback.

"Yes, I'm going out later" Rebecca replied somewhat surprised by the question. Kate knew that the box wouldn't always recognize the same arse if it was wearing different clothes. This skirt was much less restrictive and her butt would now make a different pattern on the sensor.

Again the girls went to the table and again Rebecca sat down on the box. As she sat down her short skirt rode up so that her knicker-clad butt was resting on the sensor. Kate activated the sensor but nothing happened. She kept trying but without the trousers, Rebecca's butt was resting in a slightly different way on the lid and without the exact same match the box couldn't be unlocked.

She couldn't let Nicole suffer inside the metal box all night and had to come clean to Rebecca. "I can't believe you used me in your sex games without me knowing" she exclaimed as she stood up and pulled back the table to reveal Nicole's body. "And this poor girl's been locked in here all day because I sat on her earlier" she continued.

"I have some trousers that might fit you" Kate said, "Perhaps you could try them on?" Rebecca thought about this for a minute. "I'll only help you release her if you agree for me to lock you in the box afterwards". Kate shook her head. "OK" Rebecca smiled, "I'm leaving".

Kate caught up with her by the door and agreed to her demand. Rebecca tried on a few pairs of Kate's trousers until she found a pair that fitted. She sat down on the lid and immediately unlocked the box. Kate inserted the key and Nicole was finally free.

"Now you!" Rebecca directed. Kate hesitantly put her neck through the narrow opening in the side of the box and waited for the lid to close her in. Rebecca removed Kate's trousers and sat down on the lid in just her knickers. "Now get out of that honey," she purred as the light turned red. "I'll be back sometime maybe" she smiled as she left the two friends speechless.