Karyn's roommate comes home

You lie back on the couch, hugging your friend. Friend? Lover now, you suppose.
"It looks like you need some attention too."
She's looking down at your boxers. Your dick is pitching a tent, and there's a (slightly embarassing) amount of pre stainging the the blue fabric. Karyn gives your chest a little squeeze, and reaches down to pull your dick through your boxers. Stroking it gently, her hand covered in your juices, she starts pulling you towards her entrance.
You get the picture pretty quickly.
Both of your heads snap towards the door as you hear a car pull in the driveway.
"Shit!" Karyn says "my roommate is home!"
You're both a naked mess, there's clothes everywhere, and the couch has clearly seen better days. You dive towards your pants and pull out the rock.
I wish we were in Karyn's room, and that this room was clean!"
An irresistable urge to close your eyes fills you, and when you open them again, you and Karyn are hugging each other on the floor of her bedroom.
"I'm really starting to like that thing." Karyn sighs.
The front door slams shut as Karyn's roommate enters the flat.
"Karyn? I'm home." She yells. "You here?"
You're quietly laughing with Karyn as she pulls you onto her bed. It's twin size, and neatly made.
The rock is still in your hand.
"I wish Karyn's room was soundproof."
The rock glows faintly in the dark.
"Hey, Abby?" You yell, Kayrn giving you a mortified look "me and Karyn are going to fuck for a while, are you okay with that?"
Silence. She didn't hear you.
"Jon!" Karyn hisses, still scared of her roommate.
You laugh, and roll on top of her.
"She's absolutely beautiful, Abby, and you would not believe how she tastes."
You go in for the kiss. Karyn is laughing into your mouth now.
But soundproofness goes two ways. You didn't even hear Abby walk up the stairs, so her knock on the door scares you both.
It's probably not the best way to hande things, but it's the first thing you think of.
"I wish me and Karyn were invisible for ten minutes!"
The door creaks open.
"Karyn?" Abby asks to the empty room.
You can't see yourself. And you can't see Karyn, either.
But you can sure feel her hand tug on your dick.
You do your best to stifle a little yell, and feel Karyn rocking with silent laughter.
It makes the bed creak a little, which makes Abby curious.
"Huh?" She says, walking over. She's just a few feet away from you, scanning the bed for whatever made the noise. Her eyes stop on the rock for a second, which looks as though it's just resting on the sheets.
Karyn starts stroking, and it takes all your willpower to not do anything to disturb the bed.
But two can play at that game.
You feel down her arm, follow her stomach, and start giving Karyn some 'attention' of her own. You can't see her face right now, but the bed creaks a little again.
"Weird" Abby says to herself, then sniffs the air a little. Her face scrunches up.
"Oh god Karyn, I'm buying you some febreeze" she says, turning for the door. She shuts it, and it's just the two of you again.
"For the record" you say "I could stand to smell that forever."