Zoe's plan revealed...

You each take one of Karen's arms and help her into bed.
"I'm gonna... get her out of her dress, James. Why don't you go into our room. I'll be there in a second."
"Yeah of course." You head out, and are surprised, and yet not surprised, to find Zoe seated on your bed, with a rucksack next to her. She's changed out of her club outfit, though she's kept the fishnet stockings and skirt. Her top is dominated by a black leather bustier and bra. Her arms and shoulders are bare.
"Zoe... what...."
"Come sit, James. Let's wait for Jenna."
You sit nervously.
"What's in the bag, Zoe?" You can't even begin to imagine.
"You'll see."
Jenna enters, chuckling.
"That bitch was fighting me. Trying to get that dress off her was like trying to undress Riley when she was 3." She looks at Zoe. "What have you told him?"
"Nothing yet, Jen." Jenna smiles as she sits next to you, putting a hand in your lap.
"So.. Zoe told me about what happened after our little rendezvous in the office today."
You swallow... "She....she... did..?"
"Yes baby. Don't look so scared." She kisses you gently, trying to calm your worries. "She has an idea to help you with your occasional issue..."
"It's actually very simple James. Too much porn. When you jerk off to porn, you condition your dick to orgasm with certain stimuli. Regular sex doesn't always match up with that stimulus." She unzips her bag. "So what you need to do, is retrain your cock." While Zoe's speaking, Jenna unzips your shorts, fishing inside for you dick to rub and squeeze.
"You need to do something... "porn-y" to get you close, and then finish inside Jenna, to recondition your dick to cum from the feeling of normal sex with her again." She pulls out two buttplugs of different lengths, some lube, and then.... a big black rubber strapon dildo, you estimate it's length at about 8.5 inches, bigger than you by at least an inch.
"What the...." Suddenly, you feel Jenna's mouth envelop your cock. You look down in surprise. "What is this plan?"
"Isn't it obvious? We're going to have a three-way, Jimmy."
Your brain goes blank for a second. "But... your my sister... Jenna... you can't possibly be okay with this?"
She pops up, slurping up excess spit and smiling. "I'll admit, I was shocked, and hesitant at first... but her plan makes sense, and just look at her, baby. She's sex on a stick." Jenna climbs over you to stick her tongue in Zoe's mouth, grabbing her tit and moaning. "As far as the whole sister thing.... well.... Karen and I used to fool around.... when we were teenagers... so I guess I don't see it as a big issue..."
You can't believe what you're hearing. But you aren't going to turn down the opportunity to fuck two sexy women like this, even if one is your baby half-sister.
"If this is the plan.... let's, let's do it!!"
Jenna lays you back, peeling off her dress and rubbing your cock as Zoe strips off skirt and panties behind her, and steps into the strapon harness. She slowly starts loving your cock, with languid licks up and down the shaft and swirling around the head with her tongue. Her semi-drunken state does nothing to detract from her skills. She slobbers obscenely on your cock and slowly takes it all the way down, gagging as the girth stretches her throat.
"Gggggggggg....." she gargles, and warm spit runs down your shaft.
"Ahhh....fuck baby...." You are watching Zoe as she slowly straps on the stand-in dick. She climbs on the bed, and begins to eat Jenna's pussy and asshole.
"Ernnnnn!!!!" Jenna moans on your dick, before popping free and stroking it. "Oh my....my fucking god, Zoe...your tongue....Baby she's eating my ass and it feels a-MAZ-ing..." Zoe spits on Jenna's pucker, and works two finger inside, making Jenna cry out.
"Ah!! Oh go slow, girl.... it's been a while..." she slurps on your balls, continuing her luxuriant pace on your shaft with her hand. You run a hand through her hair.
"I love you so much."
"I fucking love you too, baby."
"And I love you both!!" Zoe's spritely voice makes you both chuckle, which quickly fades back to moaning for Jenna as Zoe lubes up the smaller buttplug and works it in.
"OOOOooowwww......" her face tightens up in pain at the intrusion to her tight asshole.
"Relax, girl." Jenna shifts to lying in between your legs, and occupies herself by bobbing rhythmically on your cock.
Your conscious mind goes. All is pleasure right now. Thought is distant.
When thought returns, it's because Jenna is now squealing as she strokes your cock. Zoe is pounding her pussy with the strapon, and by the sight of the smaller buttplug on the bed, and the absence of its larger version, you can guess at the reason for Jenna's incoherent babbling.
"fuckinjesuschristoomigodomigodmigooooodddd......" her wail extends and deepens, like a cat in heat. It's the most erotic thing you've ever heard.