“Not until your sister gets here.”

A week later, her teeth gritted and twitching from a month without orgasm, donning her collar, a tight sheer top, black underwear and thigh highs, Carrie opens the door and greets her sister.

Cassidy’s sister is shocked. “Oh god.... am... am I interrupting something?”

“Nope” Cassidy smiles “this household is for having fun.”

...until she’s no longer shocked “Why am I not surprised” Cassidy says shaking her head, then stepping into the apartment unbuttoning her jeans and pulling them down.

Cassidy takes to the environment more quickly than expected. Maybe it’s because she’s always known her sister well enough to suspect this might happen to her one day. Maybe because she has a not-so-hidden naughty streak herself. Maybe both.

Her pale body looks lovely in her bra and panties. She has no objection to wearing just that with you around. She has no objection when she’s shown her room and vibrator for her visit. She has no objection to any of it.

So the 3 of you hang out, you dressed in just your boxers, Carrie in her **** outfit and Cassidy in a pink bra and cotton panties. You chill and converse as if there’s nothing unusual going on.

You order pizza and Carrie gladly answers the door dressed as she is. You eat it. You have some wine. All as if this is totally normal.

And finally you settle in to watch a movie together, you and Carrie on the couch, Cassidy lounging on the floor nearby.

For a split second you wonder what might develop next, until the sight of Scarlett Johansson in a tight outfit in the movie perks up your cock and Carrie takes notice.

“I know, right?” She says looking down at it with eager eyes. “Want me to help?”

Well, you think, your rule was no fun until her sister got her. Perhaps it’s time to finally let her loose.

“Hey Cass... you don’t mind if I take care of my man, do you?” She asks, probably to intentionally draw attention.

Cassidy looks back at you two and shrugs. “I expect nothing less of you.” And she turns back to he movie, expecting to ignore what’s going on.

That turns out to be harder than she planned with the sounds of her sister sucking and slurping on your cock filling the room.

“Are you just gonna ignore this?” Carrie asks her sister, with a mouthful of cock.

Cassidy shrugs looking ahead. “Done it before. Remember that time I visited you in college? When that guy came into the room in the middle of the night?”

“It’s okay, you can tell the true story. He knows what I’m like” Carrie interrupts.

“Okay, when those guys came into the room in the middle of the night. Well I ignored you then.” Cassidy insists.

“No you didn’t” Carrie retorts. “I heard you rubbing yourself off. Not that it matters. Those guys were dopes. You didn’t miss much. But now you’ll be missing the nicest cock that you may ever see.” Carrie jerks you, slathering her spittle all over your member. You know she’s eager to delve in for more. “Cmon up here and help. What’s the worst that can happen?” She asks of her sister.

“With you?” Cassidy responds still focused on the t.v. “I can only imagine.”

Suddenly Carrie pounces down to the floor next to her sister, whispering in her ear. “Have you? Have you imagined?”

You see Cassidy’s body tense up “imagined what?”

“About me?”

“What about you?”

“Anything about me” Carrie is going in for the kill. Her fingertips find their way onto her sister’s upper leg, caressing up to her thigh and down to her knee.

And Cassidy is starting to drop her guard. “You’re insane.”

“I am. Have you imagined what it’s like to be insane?”

“I’ve... I’ve wondered what it might be like to be you” Cassidy admits.

“Well now is your chance” Carrie says “no one outside this room ever has to know.”

The room fills with silence. There’s a wild tension. You sense Cassidy is thinking. Thinking hard. Maybe trying to convince herself to do what she wants deep down. Your cock still throbs, hard as ever, pointed up at the ceiling.

And finally Cassidy turns to look at it. Carrie wears a big smile.

“Now go and tickle...”

“Shhhhh” Cassidy bushes her sister. “I know how to suck dick.” She crawls the 2 feet over to you, makes brief eye-contact, licks her lips slightly, licks her lips more and finally slides them around your head.

Carrie watches with total glee.

Cassidy slides her mouth down your shaft. You feel her tongue dancing on your sensitive skin. Then she starts to bob, over and over, making slurping sounds similar to what her sister was making. And she moans.

“Mmmm”

“Don’t forget to give the balls some love.” Carrie says as she watches with adoration.

Cassidy pulls her lips off you with a popping noise. “I know” she says, sliding her tongue down to your scrotum and making it wet.

“Don’t forget to give the asshole some love.” Carrie says.

Cassidy glances over at her sister. For a moment you think she’s going to resist. But maybe she’s just making sure she’s watching closely as her tongue takes a trip past your taint and starts to lick up your asshole.

The sensation is great. Your cock is as hard as it’s ever been. Cassidy too seems to love it, licking at you with reckless abandon, almost penetrating your asshole with her tongue once or twice. And she doesn’t seem to mind when she feels her sister place a hand on her head to guide her.

After a few moments she pulls back, almost dazed, like she’s in a **** fueled high.

“This is almost what it’s like to be me.” Carrie whispers to her sister, leaning in close. “But there is one more thing.”

“Yeah?” Cassidy mumbles.

“Look up at him.” Carrie tells her sister. And Cassidy does. Damn, she’s so pretty. Both girls are. This moment is pure insanity. “Repeat after me.” Carrie continues “I am your ****.”

And here Cassidy does hesitate. But you kinda love that. It’ll make it even better when she gives in, which you know she will. “No one outside this room ever has to know?”

“Say, ‘My only true purpose in life is pleasing you.’” Carrie goes on “And doing whatever you want.”

Cassidy takes a deep breath. “I am your ****. My only true purpose in life is pleasing you and doing whatever you want.”

Does she know what she’s getting into? You wonder. She has to. She just finished eating her sister’s boyfriend’s ass while her sister watched.

“Now call him Master.” Carrie says, almost demands.

Cassidy giggles. Your life is complete. “Master... what do you want of me?”

And you can think of a million things