"Um... no, no one else"

Tess gives an uncharacteristically sheepish smile. Then she glances down, indicating her thoughts are at the wet excitement between her legs. "Anyway, you were doing a good job down there. Would you like to continue the show?"

Katie nods and smiles. She licks her lips, takes a breath and starts to lean in.

"Wait a minute" you say, feeling suspicious. Katie pauses. You can't believe you're halting the moment. You do want to continue to watch your girlfriend discover her sister's pussy. But you have to press the point. "I don't think I believe you." You say.

Tess blushes a little. You know you're right.

"Who else have you been with?" you demand, not forcefully, but playfully.

"I... um... no one... you don't want to know." She stutters. Tess is not prone to stuttering. She's goofy and occasionally awkward, but not a stumbling nervous person.

"I do want to know." You insist. Katie straightens herself back up. She's not going in until Tess comes clean.

"Okay." Tess says. "Candace."

For some reason it takes you a second. Who is Candace? you think. You only know one Candace and that's your sister. But who is the one that Tess is talking about right now?

Of course you figure it out. Katie does too, she puts her hand over her mouth in shock.

"You fucked my sister?" You ask Tess.

She squints, trying to read how you're feeling. You're not even sure how you're feeling. "Yyyyyes." she says.

"How do you even know my sister?" You ask.

"I met her at your housewarming party." Tess says. "We talked a little bit. I friended her on facebook."

"Wait a minute" you say, realizing something "My sister has had a boyfriend for like the last 10 years. Does he know?" You can't imagine Candace cheating on Eric with another girl. You can't imagine Candace with another girl at all.

"Yeah. He was there." Tess says. "Look, we were just kinda talking about... fun things one time and I said 'if you and Eric ever want to see if your bed can fit three people, I hope I'm the one you call' and she called me the next day." Tess shrugs.

"Wait... we have to know more than that." Katie insists. But you're not sure you do want to know more than that. You do because you're curious exactly how Tess pulled this off with your usually serious sister. But you don't really want to think of her in such a sexual capacity... and of course you realize you're thinking this as your girlfriend and her sister, sit across the room from you, doing what they're doing. This night must be very, very strange for them. "Don't you want to know the details?" Katie asks you.

You don't have an answer. "Maybe." you say softly.

"Okay" Tess answers with a big grin, her timidity turning into bouncy confidence. "I'll tell you the details, and I have a great idea."