“I need to masturbate,” Sophie murmured under her breath.

I should explain: we visited a lingerie store in a local seaside town. I had offered to buy Sophie some new knickers as we had already ruined hers on the train down with my hand up her skirt playing with her clit through her lacy panties then jamming two fingers up her flooding cunt. Browsing through the racks of thongs and every conceivable variety of knickers she had become increasingly turned on by what she might get up to in them.

“I gotta get out of here,” she whispered to me.

“Well, which ones do you want?”

“These.”

Sophie grabbed a pair of purple Brazilian cut panties and handed them to the smirking sales girl. She took rather too long packing them so Sophie grabbed them, stuffed them in her handbag, paid, and left with me in tow.

“I’ve got to put these on right now.”

Sophie sat down on a park bench and slipped off her sodden panties. Reaching into her bag she pulled out the new purple pair and proceeded to put them on in the public park.

I wasn’t sure if any of the dog walkers could see her pull them up tight into her cunt.

“I can’t wait until we get home, I’ve got to get off right now.”

I was somewhat alarmed as we were in a totally public area with couples and families playing in the park. How was she going to achieve this?

Sophie opened and shut her legs revealing the already damp crotch of her new panties as she syntribated her cunt.

I was sure that the young couple on the park bench opposite could see her crotch as she squeezed her thighs together then opened and shut them quickly. Sophie forced her wrist hard against her pubis and she began to whimper under her breath.

“Fuck I’m coming, coming, coming," she bit her lip as she looked me straight in the eyes, a pleading expression on her face, as helpless to stop now she spasmed uncontrollably, her thighs shaking.

Abandoning all modesty, Sophie opened her legs wide and tugged at the sodden crotch of her new, purple panties. The couple opposite was now staring at her brazen sex, their eyes on stalks as she gave in and orgasmed in public. I couldn’t help noticing the girl opposite was opening and closing her thighs involuntarily just like Sophie was.

Their eyes met just as she flooded the crotch of her panties in front of me and the young couple. Sophie was past caring now and let out a long sigh of satisfaction as her thighs closed over her hand and her eyes wide shut in bliss.

When she recovered a little, Sophie slipped off her ruined, new panties and held them up for me to drink in her sexy smell.

“Want these to add to your collection or shall I dump them in the bin?”

Well, I thought, they were too good to waste and a keepsake from her was a good turn-on for later use, so I stuffed them in my pocket.

She smiled at the young couple as we left, they didn’t know where to look.