Stacy lay beneath her brother, her legs spread wide for him, her slim hips moving vigorously in time to his thrusts. Her pretty little snub-nosed face was twisted into a horny leer, her little pink tongue flashing out to lick her lips. She was clinging hard to Mark, digging her nails into his sweaty shoulders. With the door open, Karen and Bill could hear her words distinctly.
"Oooo, yeah, Markie," she squealed, "do it to me… That's so good… You're the best, big brother, the best fucking lay in the world…"
Mark's body lunged up and down over his naked sister, his rosy stiff cock zipping in and out of her cunt and gleaming with her juice. He was ginning happily, panting, sighing.
"You're the best, too, baby sister," he said hoarsely. "You got the tightest hottest little box I ever fucked… Oh, man, yeah… It's out of sight…"
Karen looked like she was about to scream, so Bill clapped a hand over her mouth and dragged her down the hall, out of the kids hearing.
"Listen," he said, "we can't just go rushing in there. We have to talk and decide what to do. And we have to be totally honest with each other." He stopped for a moment, and Karen noticed that his face was pale and sheepish-looking.
"Karen," he said haltingly, "I'm terribly sorry, but I have to tell you this. I'm not excusing myself, I'm just telling you, so you'll know about it when we face those kids. I… I made love to Stacy at the beach today."
Karen fell against him, weeping. "Oh, Bill," she said miserably, "I'm just as guilty as you ate. While you and Stacy were gone, Mark and I made love. I'm so sorry. I knew it was wrong, but…"
"Never mind," Bill said, giving her a reassuring hug, "I know how it is. The point is, what are we going to do now?"
"Well, we can't let them make love," Karen said. "It's horrible – brother and sister. We've got to stop them, make them understand that it's wrong."
"I agree," said Bill. "We can work on that other problem later. I mean about us and the kids. Come on."
They hurried back down the hall and peered out of the shadows into Mark's room. Mark and Stacy were still hot at it, fucking joyfully and furiously. Now Bill and Karen could even hear the soft lewd squishing noise of Mark's thick meat in Stacy's tight wet box.
Somehow that noise made Karen feel hot and horny all over. She knew it was wicked, but it just turned her on powerfully. She felt her cunt contact sharply in sudden arousal, and then a steamy trickle of pussy juice ran down her thighs.
Bill had the same reaction. That intimate wicked noise jolted him with lusty arousal, and he felt his cock going rock-hard in his pajamas, tenting his crotch obscenely. Jesus, watching those kids fuck was a real turn-on…
Bill and Karen hesitated just outside Mark's door, reluctant to break that strange spell. Watching the handsome brother and sister ball each other was tremendously exciting. Lust made the adults hesitant and confused.
"You come yet?" Mark asked his sister.
"No," Stacy panted, "I don't want to yet. I want this to go on and on."
"Me, too," said Mark. "I got a cock-stand that won't quit. How about having it another way, just for fun?"
"Sure," Stacy said eagerly.
Mark lifted himself off his sister's cuddly warm body and gingerly withdrew his aching hard-on from her creamy little twat. His cock was rosy-red from the friction of their hot fucking, and it snapped up to hug his belly.
Karen gazed hungrily at her nephew's wonderfully stiff cock. My God, what she wouldn't give to change places with Stacy, to have that rigid fat boy-cock thrust hard up her starved cunt. She almost moaned aloud at the thought of it, and more hot cunt juice ran down her inner thighs.
"Let's do it dog-style," Stacy giggled.
"Fine by me," Mark said, grinning.
Stacy rolled over and stuck her cute little butt up in the air. From the dark hallway Bill could see his adopted daughter's delicious little pink pussy, wet and open and eager. His cock lurched with horny longing and drooled a big drop of juice. Christ, how he'd like to be in Mark's place, shoving his swollen dick into that fiery little box of hers…
Still grinning, utterly without shame, Mark knelt behind his sister and wedged the big hard purple head of his cock into her tiny, soaked cunt mouth. He just held it there a moment, teasing her, and Stacy whimpered and twitched her ass impatiently.
"Come on, motherfucker," she laughed, "get it in there… or have you fallen asleep?"
"Not a chance," Mark chuckled. "Hang on, Sis… you're gonna get some cock right NOW."
He pushed hard into her, and Karen and Bill watched hungrily as his fat pink prick shot up his sister's tiny hair-fringed twat. Stacy moaned hoarsely and raised her cute little ass even higher to take his thrust. His swollen rosy balls came to rest against her pussy.
"Ooooo," Stacy howled. "Oh, YEAH… Now fuck me, Mark, fuck me hard…"
Mark seized her slim hips to steady himself and started balling her in deep swift strokes. His freckled face flushed with horny pleasure, and he grinned and panted. By now Stacy's lusty little box was so creamy that his thick meat made a very loud slurping noise as he reamed her.
Karen staggered back against Bill, dizzy with longing. Just as horny as she was, Bill slipped his arms around her and cupped her big melon-size breasts, squeezing them hungrily through the thin silky material of her nightgown.
"Oh, God, Bill," she whispered huskily, "I don't know what's come over me, but I feel so… so strange. I don't want to stop them just yet."
"I know," Bill said, his voice raspy with longing. "I feel the same way. Let's just stand here and watch for a while. The harm's already done anyway. We might as well let them finish."
He tugged Karen's flimsy nightgown down off her shoulders and breasts, and she didn't stop him. She wanted to feel his scorching hands on her naked tits. She stifled a moan of pleasure when she felt him cupping her big throbbing jugs, squeezing them almost painfully hard.
Bill pressed his body against hers, and she felt the long rigid line of his erect cock against her ass. She shuddered with excitement. She reached back, fumbled around, and finally touched his tented fly. She feverishly rubbed the rock-hard pulsing line of his cock, feeling its fierce heat through his pajamas.
"Baby, baby," Bill moaned.
Meanwhile Mark was working up a good sweat as he vigorously balled his little sister. He liked the canine position because he could watch his cock going in and out of her, watch how it stretched her little pink pussy lips and drove cleanly into her right up to his balls. It made him feel powerful and commanding.
Stacy helped out with her appreciative cries and the horny jerking of her hips and the furious hot creaming of her tight cock-stuffed cunt.
"Oh, yeah, Markie," she whined, "ball me, fuck meee… Shit, that's good… I love it…"
"Well, you're gonna get lots more, little sister, before his night's over," Mark panted. "I really dig balling you. Honestly, Stacy, we should have thought of this a long time ago…"
"I know," Stacy sighed, "I know…"
In one part of his mind Bill realized how scandalous and strange the scene was, he and Karen watching their adopted son and daughter fuck, getting hotly turned on themselves. Decent parents would have run right in there, pulled the kids apart and punished them severely. It was sick to just stand there and enjoy it.
Well, so it was sick. So he didn't want to be decent. To hell with it. He and Karen had been middle-class and decent all their married life, and what good had it done for them? They bored each other in bed – that's what it had done for them.
Now, however, watching Mark lustily balling his kid sister, they were getting powerfully aroused. For the first time in years Bill found excitement in fondling and squeezing his wife's huge ripe tits. Karen groped hungrily for his cock, turned on to him for the first time since he could remember. Yes, this scene might be "sick" to other people, but it was doing his marriage a lot of good.