"Taste every inch of her."

Your instruction is calm and collected. You're proud of that, because inside you're still freaking out at this whole situation.

Katie reacts with a nod. She knew this was coming. She has to have prepared herself for anything tonight. It has to be an odd mental state for her to be in. Part of you can't wait until some future date when you're cuddling in bed having one of your late night chats, asking her exactly how this all came to plan.

But most of you is happy to be where you are right now.

Kate looks at Tess, nods and cocks her head a bit, as if to say 'here we go.' And helps Tess off with her shirt. Tess raises her arms above her head and within moments, her sister is staring at her topless torso.

And so are you. Tess's breasts are amazing. You've never spent that much time thinking about them because, well she's your girlfriend sister, what would be the point? But looking at them, perky big b-cups, with large nipples, you think they might be the nicest pair of breasts you've ever seen.

Katie takes a deep breath, leans in and gives Tess a kiss on the neck. Not just a peck, but a long, passionate, tongue-filled slick across her neck. Then she continues on to her shoulder, onto the top of her chest, and finally coming face to face with her wonderful tits.

Tess says nothing through it all. She just watches, her breathing getting increasingly intense.

But Katie says something, as she stares at her sister's breasts, just a few inches away. She giggles a bit and says "Hey, you've got a birth mark right next to your nipple."

Tess smiles. The comments lets some of the tension out of the room. "You've seen me topless before. You never noticed that?"

Katie rolls her eyes. "Yeah, in changing rooms and stuff. How closely do you think I was looking at your boobs?"

"Well don't you regret that now?" Tess responds. The tone of this is their classic sister banter. Except it's usually not about nude escapades.

"Do you want to sass me or do you want me to lick this birthmark?" Katie gives a playful ultimatum.

"Okay, fine" Tess says, leans back and closes her eyes.

And you watch with total attention and a massive erection as your girlfriend cups her mouth over her sister's right nipple. You can't necessarily see what's going on behind those lips but the soft purring of Tess tells you it's pretty wonderful. And you can see as Tess's other nipple hardens right before your eyes.

Tess unzips the sides of her long skirt and quickly pulls it down off her legs. If she was wearing underwear she's pulled it down as well. Clearly she's not interested in delaying what comes next.

You want to pull out your throbbing cock and start jerking right then and there. But you know this is just beginning. You tell yourself to stay cool and patient.

Eventually Katie pulls her mouth from her sister's nipple, a strand of saliva, stretching out to it as it moves away. Then she continues to kiss down Tess's body, past her navel, past her waist, until she's kneeling there staring at her sister's pussy.

From your spot you can't quite see it. But you can imagine it's a beautiful thing. Katie just stares as Tess slowly spreads her thighs, breathing very, very, heavily.

For a moment you wonder if she's waiting for another instruction. So you start. "You should..."

"I know what to do next." Katie says, turning to you with an excited but apprehensive smile on her face. "Don't worry about me. Give her some orders if you want." And with that Katie's face leans in and buries itself in her sister's crotch.

You want to watch this forever, even if it's just the image of the back of a head between two thighs. But you realize that Tess is looking for you. Just like Katie said, she's expecting orders