One weekend we drove to Chicago to visit Dad’s parents, leaving Friday evening and riding late into the night. Caitlin and I rode in the back seat, and after a while Cait pulled a blanket over herself and stretched out, resting her pretty head on my thigh. I ran my hand affectionately through her velvety close-cropped hair, and the sensation, together with her warmth against my thigh, began to turn me on. When she rolled over to get more comfortable, she must have noticed my arousal, so near her face, and it spurred her to mischief.

She pulled the blanket up further, covering her head and my crotch, and I wondered what she would try next. I was both titillated and worried by the thought that we could get busted so easily, but the ‘rents were oblivious, grooving to their old Sting and Simple Minds CDs on the stereo.

At first I sensed only a pressure against my crotch, but then I felt the little purring of my fly being unzipped, and a hand palpated my straining cock through the fabric of my briefs. Just when this got really uncomfortable, Cait deftly freed my erection from its prison and began to stroke it like the expert she was becoming. Next thing I knew, the warmth of her mouth engulfed me, and I even felt a little painful-exciting brush of her teeth. I almost yelped, but managed to turn it into a cough, and she let out a girlish giggle.

I held the blanket up a little so that the bobing of her head wouldn’t be too obvious through the rear-view. The thought that my little sister was gobbling my penis right here in the family car was thrilling. But of course I had to try not to make any obvious noises, and Cait was clearly enjoying my struggles against the power of her naughtiness. I was sure I could hear slurping sounds coming from down there as she lapped and swirled her tongue around my throbbing head. I risked reaching under the blanket to cup one of her full breasts, squeezing it, and pinching the nipple, and this time she was the one who had to suppress something between a moan and a squeal.

I lifted the edge of the blanket enough to peek at my cock going in and out of her lovely innocent mouth, and then it wasn’t long before I felt my climax approaching and hoped my sister knew what she was doing; I didn’t know how we’d explain a big old semen stain on the seat and blanket. But Cait had it figured out: she kept pumping my cock deep into her mouth as I spurted what felt like a pint of cum between those soft and sensuous lips. She let out a couple of muted gagging sounds, but managed to swallow most of it, letting the rest dribble in a sticky (and oh so sexy) trail down her cheek. I fished out a Kleenex and helped wipe her off as she grinned wickedly up at me.

Caitlin was just sitting up, with her best demure schoolgirl expression on her face, when Mom turned around and asked, “Hey kids, are you up for a bite?”

There wasn’t much chance for mischief in my grandparents’ house, full as it was of aunts and uncles and cousins, though Cait took some sisterly liberties, walking into the kitchen where I was seated at breakfast and giving me a hug that rubbed her braless breasts against my face or sitting in my lap to watch a movie with the family. I have, let’s just say, no memory of what the movie was about.

But my main focus was the shopping outing that I had planned in conjunction with Megan. I told Cait that we were headed downtown but nothing more, except that Megan and I were going in on an early birthday present for her. We walked through a hipster neighborhood of coffee shops and tattoo parlors, and when I stopped in front of a shop, Cait let out a snorting laugh at its name: Puss in Boots., and at the display of toys and gear in the window.

“Sean, are you serious? What are we going to buy here?”

“You said you had a fantasy of taking Megan the way a man does. We’re going to get you some junk of your own.”

“Wha? Oh, he heh.” A blush began to spread across her pretty face, and then a slightly crooked smile, starting at the corners of her mouth and gradually turning into a lewd grin. “And Megan is down with this?”

“Oh yeah, I said the present was from the two of us. I’m providing the money, and she’s providing the, uh, the experience.”

“Oh yeah, wow.”

She was practically bouncing on her toes as we walked in, though still blushing in a most fetching manner. I suppose I must have blushed too. I mean, it’s not as though I’d ever been in a place like that either. But the staff were very kind and enthusiastic, and I got the feeling that the woman who helped us, a slender hottie with pink hair and a tongue piercing that slurred her speech a little, was excited by the idea of introducing this fresh-faced young thing to unexplored pleasures.

It turned out there were lots of decisions to make, and Cait got a look of earnest concentration on her face as she groped and fondled the different models of strap-on. She finally settled on one with thigh straps, which the tongue-pierced hottie said would give her better control and thrust.

“Thrust, huh?” Cait said. “I could go for thrust, I think.” And she licked her lips.

As we walked home, Cait put her arm around my waist and I put an arm around her shoulder, feeling her warmth against me, and the slight pressure of a side-boob. I could also feel a new swagger in the way she walked, here in the big city where nobody knew her, with her brand-new cock and balls dangling in a bag from her shoulder.

We decided to wait to deploy the strap-on until we could have the place to ourselves and make as much noise as we wanted. Fortunately, our parents had a tradition where they’d gather each June at a cabin with some other couples they’d known forever for a weekend of drinking and fishing and doing whatever middle-aged people do for fun. At last the day arrived and Cait and I waved them off with some impatience.

On Saturday morning I came down to breakfast and found Cait standing at the counter wearing a bathrobe and a big black hard-on. As I hugged her from behind and gave the dildo a few wrap-around tugs, she explained that the instructions had recommended wearing it around the house to get used to the feel. I found the look a little comical and also super sexy, and as I stroked the cock and began to knead her breast under the robe, my own erection was growing and poking her shapely little ass. But she shooed me away, telling me I’d have to wait till Megan came over.

We had planned to make a nice spaghetti dinner and even procured a jug of red wine, but when Megan appeared at the door, radiant in a sleeveless short black dress, stockings and heels, her green eyes sparkling with mischief behind dramatic mascara and liner, we fell upon her greedily. I kissed her, our tongues wrestling as I turned my head to the side so that I could thrust my tongue ever deeper into her hot mouth while I cupped the back of her elegant neck with one hand. Meanwhile, Caitlin embraced her from behind, kneading her pert breasts so that moans passed from Megan’s mouth to mine and nibbling at her earlobe behind her dangling earrings.

It was obvious that dinner would have to wait. We all went upstairs, Megan and I to the grownups’ room, which had the biggest bed, and Caitlin to her room to get in character. Megan and I wasted no time undressing each other. She removed my shirt and licked and nibbled at my nipples, making me squeal a little, then unzipped my jeans to free my already-hardening cock. I pulled her dress over her head to reveal her flat ivory belly. When I helped her remove her panties, leaving her sexy stockings on, I learned that she had prepared a surprise for us: her pussy was shaved smooth. I was fascinated, first petting the soft skin with my hand and then kneeling so that I could rub my face against her mound and feel the smoothness on my cheek.

At this point Cait entered the room all dressed up in chunky work boots, a cap advertising a chain-saw manufacturer, and a Carhart jacket left open at the front to reveal the curve of her lovely bare breasts beneath. And of course her big black cock. She was already excited, cheeks flushed and chest thrust out as she strutted up to us and said in her throaty soprano:

“OK, bitches. Get down here and worship my big cock!”

I had to fight to keep from giggling at this new domineering Caitlin, but Megan dropped to her knees and looked up into Cait’s eyes as she took hold of the big cock. She guided it with one hand between her luscious lips, moaning, “Mmmg, ommm,” as she licked the head and began to bob up and down on it, while Cait encouraged her:

“Oh yeah, suck it, suck it, you are so fucking sexy with my cok in your little mouth. Oh yeah, let that drool run down your chin like a little slut.”

I decided to join in my baby sister’s fantasy, and came up beside Megan. She let me have a turn on the dildo, which was already warm and glistening with her saliva. I took the head in my mouth and licked the rubbery underside, then Cait began to pump it deeper into my mouth, gripping my hair with her small hands. I started to make exaggerated gagging noises and this seemed to drive her wild:

“GaGha, ghe glug gallagla!”

“Oh, gag on it, choke on my big prick, you little whore! Take it down your fucking throat!”

It filled me with pleasure to see my little sister living out her butch dream with us, but I also figured it was time for Megan to take a turn before I really started to choke. This also gave me an opportunity to explore Megan’s body and feel again her wonderful hairless cleft with my fingers. As I massaged her vulva, I could hear that her moans were no longer just play-acting.

On my next turn I could smell Caitlin’s sex, which must have been wet with the drama and the friction of the dildo’s base against her crotch. Soon she commanded us to take off her boots, and we bent down obediently to unlace and pull them off in turn. Shrugging off her cap and jacket, she pointed to the bed and demanded:

“All right, girlie, are you ready to be fucked?”

Caitlin lay on her back on the bed and Megan climbed on top, straddling her. I lay by their side and looked into Megan’s face as she lowered herself onto Caitlin’s new dick with a look of intense concentration, her delicate brows furrowed and her tongue peeking out of the corner of her half-open mouth. Then I watched in rapture as Caitlin’s dildo moved in and out between her puffy, swollen labia.

“Gnk mmmk ahh,” Megan grunted, leaning forwad and letting the dildo sink further into her sensitive vagina. Caitlin grasped her flared hips and at first tried a bit awkwardly to thrust upward, but soon got into a rhythm. Then she rolled Megan over and bore down on her in classic missionary style. I reached over to caress Caitlin’s back and ass, and I could feel her butt muscles clenching with each powerful thrust. She was breathing heavily now, and Megan egged her on:

“Come on, Cait, you big butch! Fuck me with your hard cock, fuck me deeper! O god, o fuck yeah, o you sexy dyke, give it to me now!”

After a few minutes the big thrusts modulated into grinding and moaning as Caitlin rested her weight on Megan and their tits mashed into each other. Cait’s moans started to take on that breathy whimpering quality that I knew meant an orgasm,, and she kept making little twitches, rubbing her pussy against the base of the dildo and grinding against Megan’s pubis, as they both came for what seemed like several minutes.

They collapsed in a sweaty heap next to me and I thought the show was over, but Cait climbed over me and embraced me from behind, and Megan drew my face closer and began to kiss me. She brought her hand to her crotch and then wrapped her dainty fingers around my dick, lubricating it with her own juices and beginning to stroke up and down on my erection.

At this point I got another surprise, as I felt Caitlin’s dildo poking between my thighs. She started to pump it, and I loved the feeling as it bumped up against my balls, rubbing them from below. Caitlin hugged me with her surprisingly strong arms, and I could feel her lovely tits pressing into my back and sense her hot breath on my neck.

Megan brought my face down to her petite breast, and I sucked eagerly at her nipple while she stroked my throbbing penis faster and faster with her shapely manicured hand. It wasn’t long before I let out a cry and exploded, defiling Megan’s pristine belly with my hot jizz.

At this point Caitlin climbed over me again and ran her dildo over Megan’s stomach, coating it in sticky semen.

“Come on, bitches, lick me clean,” she said, and Megan and I happily obliged this last bit of fantasy, tasing my cum and her pussy juice, and kissing and licking each other’s faces in case there was a last drop to be picked up.

And with that, Cait transformed back from bossy butch to my adorable baby sister, hugging us, covering our faces with kisses, saying:

“Oh thank you, thank you, this was the sweetest birthday present ever ever! I love you guys so much.”

And I could see tears in her eyes when we all lay back down and cuddled like a pile of puppies, until someone worked up the energy to go fetch the jug of red wine.