"I only need you there to pull the string when I shout."
"I'm your sister. I can't help you fuck your wife."
Jane looked panicked, pacing briskly around my kitchen wearing her uniform and distinctive high visibility jacket.
"You're also a paramedic and that's mostly why we need you, in case something goes wrong."
"This is bizarre and, frankly, disgusting. I don't know why Emily agreed to it."
"She enjoys trying new kinks, sis. Please don't judge us."
My sister relaxed. We were close, and she always wanted the best for me.
"She has agreed to this, though, right?"
"Yes, of course."
"Okay. I'll be here tomorrow morning and reverse the ambulance up to your garage. You can fuck Emily in the back of my truck, that's between you and her. I'll stand outside holding the string."
I agreed some would think my request was a disgusting idea. A friend in the Army described it to me. His girlfriend, a flight attendant, was into fringe sex activities in a big way and this was one sex-periment they'd enjoyed together.
The next morning, I reassured my wife while I took the meat from our fridge and cut off what we needed.
"It'll improve the sensation for both of us."
"I know, but should it be raw or cooked?"
"I think we should try raw. Jane's almost here, so let's get the string and get ready."
My sister backed her ambulance up to my open garage, making sure nobody could see inside. We had a reasonably long driveway, so I wasn't worried and didn't really care.
Emily was more concerned and seemed skittish.
The back of the ambulance was warm when we stepped inside wearing only our underwear. My wife smiled nervously at Jane, who avoided eye contact with me, focusing on the welfare of her sister-in-law.
"Are you sure about this, Em?"
"Yeah, I'm scared, but I want to try it. I read up on the internet and it sounds amazing."
"I'll be right outside, so scream if you need me."
My cock was already hard just thinking about what we'd planned. Emily stroked my shaft, squeezing copious lubricant from the bottle and massaging it all the way from my glans to my balls, having stripped my foreskin back.
She hated anal sex without my cock being fully lubricated.
When satisfied, Emily lay on the ambulance bed and I lifted her legs up high to secure both feet in the metal frames that usually held plasma and blood bags.
I struggled and could tell my wife was uncomfortable in her restraints.
"Jane, can you help us for a minute, please?"
"What the fuck?"
"I can't get Emily's legs secured."
"Em, you're better off standing up for this, if you ask me."
"Okay, but can you stay with me, please?"
"And watch my brother fuck you?"
"Sorry, but yeah. I'm getting cold feet."
"Oh fuck, you pair are as mad as hell."
Emily passed the string to my sister and flipped herself over, then placed her feet on the vehicle floor, laying her torso on the stretcher.
I had clear access to my wife's anus.
"Can you hold the string till we're ready?"
"Fucking hell, you'll ask me to lube your ass next."
"Would you mind? Your brother is rough and right now he's too excited."
"Don't ask me to touch his cock, Emily, or I'll shoot you both up with battery acid and tell mom it was an accident, which it won't be."
Watching my sister squirt lubricant into her palm, and walk around behind my wife to a position where she could mount her like a stallion was the most erotic sight of my life.
"I'm easing my finger inside you now, Em."
"Okay."
"Oh, oof... fuck, Jane. That's so much gentler than your brother."
I watched my sister rub Emily's spangled taboo pleasure hole, swirling her finger across its tiny ridges, pressing the rim centre gently before sliding inside up to her first knuckle.
Jane fucked my wife's ass slowly with a single finger from one hand while pressing the other palm on Emily's back as if pinning her down.
"How does that feel?"
"How much of your finger is inside me?"
Jane inspected Emily's ring-piece as she might do with a casualty.
"Two knuckles."
My sister fucked my wife slowly, squirting more lube onto her finger, then sloppily forcing it inside with each insertion, until the digit slid easily and freely.
"Do you want another finger inside you, Em? Just to make you wider before Rambo squeezes his cock in."
"Oh god yes, please."
Jane smiled at me ironically, shaking her head and I couldn't help but see the humour.
I stroked my cock, which was as solid as a steel bar. I was an audience of one to a surreal erotic theatre that I'd never considered, even in my smuttiest dreams.
Jane squeezed more lube onto her second finger, transitioning to slide two digits inside my wife's ass.
Emily groaned with delight, spread her legs wider and relaxed heavily into the cushioned stretcher.
"Grab the handrails on the side, Em."
My sister helped my wife find steel rails that Emily gripped to maintain her position.
It was about to get rough.
"I'm ready for his cock."
I stepped up behind Emily, pushing my rigid, veiny shaft past her pre-finger fucked, spangled hole, spurred on by her grunts and moaning as my glans stretched her anus and rectum wide open.
My sister shuffled back to Emily's head, moving her hair out of the way, cradling her chin in solidarity.
The women had been best friends since primary school. Jane introduced me to my future wife in the playground when we were ten years old.
"You should swallow it now, Em."
"Okay, but can you feed me, please?"
I could tell Jane was reluctant, but she understood our kink might get dangerous and her instinct to help us both had kicked in.
"Fucking, fine."
Jane unravelled the string, making sure it didn't touch the floor because hygiene was crucial.
"Take this whole, Em, then keep swallowing it."