Katie was so excited to try on her new purchases when she got home from shopping with her mum. She ran straight to her bedroom with the bags, while her mum cracked open her usual bottle of white wine. At sixteen, Katie wasn't quite old enough for that yet, but she was old enough to wear her first thong, and she couldn't wait to feel what proper grown-up underwear felt like. All her friends wore them and she didn't want to be left out.

Opening the bag, she found her prize nestling in the bottom, along with another small bag from the same store, which her mum had put in there by mistake. Pulling out the little white thong and another pink one, and laying them lovingly on her duvet, Katie took a peak inside the other bag revealing her mother's floozy purchase. It was a black lacy g-string with a sheer panel at the front, dovetailing into a narrow silky V where it would pass in between the legs. Then the bum had a gap in the lace it at the top, which would outline her teenage bottom perfectly.

“Dare I?" She wondered, holding it up to the light and admiring its skimpy construction. Compared to her cotton ones it looked more like the real thing. Maybe a size too big but they were both quite petite.

Katie knew that her mother had a new boyfriend, having been separated from her father for a few years, and she was glad about that, but a bit jealous of the time she was spending with him. Well, he obviously appreciated a good pair of knickers.

“Serve her right for forgetting all about them, I should be the one buying new knickers for a boyfriend.” She reasoned. Katie didn't actually have a boyfriend, but she had her eye on a boy and they had a date on Friday night. That's why she persuaded her mother to let her buy a thong in the first place. She had been looking forward to wearing her hard-won purchase, but this accidental small piece of fortune was altogether a more tempting idea.

Wriggling out of her super tight jeans and teenage knicks, Katie stepped into her mother's special thong, the one she was going to exhibit herself to her boyfriend in. She pulled it up her long legs and high up over her hips. Now it would be Katie who was showing off her young body, whose subtle curves had blossomed into those of a young woman almost overnight.

Now she was going to prove just how grown up she actually was. She was amazed at how the black lace and sheer silk slid between her cheeks, how it hugged her minxy (as she called it). OMG, so that's what it was all about!

She remembered her best mate giggling about surprising her boyfriend with a thong that she had bought, that had driven him crazy. (Katie was still a virgin but lots of her friends weren't).

Could she wait for Friday, or should she have a little play now? Katie had been masturbating secretly for a while, but usually, it was more a question of working out her pent-up feelings and getting some relief rather than actually enjoying herself. This was different, she felt like a real woman at last and she was determined to enjoy it.

Turning 'round, she admired her perfect bottom in the mirror, the cheeks divided by the line of her mother's lace back thong. She could feel the insistent pressure of the narrow crotch between her legs. Adjusting the ‘O’ in the bum to frame her exquisite cleft slightly, (it was probably one size too big), she pulled it up tight over her minxy, amazed by how it almost revealed her, but not quite.

Moving the material back and forth produced the most delightful sensations. This wasn't going to take long. Katie knelt on the end of her bed, resting back on her heels and admired herself in the mirror.

“OMG I really do look the business; some boy would love to get his hands on me now. Well, I'm saving it up, but I might just have a little go…"

Her index finger toyed with her emerging clit over the silky material, what there was of it. It was so easy just to slip her finger underneath and into herself, much further than it had been previously. Before she knew it Katie was rubbing her clit enthusiastically with a mounting sensation of overwhelming heat and joy between her legs. She raised herself up on her knees bucking her hips back and forth, her fingers a blur on her clitty as she ruined her mother's new thong with her first proper orgasm.

"Never mind." She mused as she collapsed back onto the bed, exhausted with it all. "I'll just pretend mum forgot to pick it up in the shop and keep these for my own use."

Later her mother, looking for her new purchase for her hot date with her boyfriend, could only find her daughter's white cotton thong in the bag. It would have to do. She could always buy her another one. Her new boyfriend seemed to be rather turned on by the choice as it turned out.