Brief Backstory: The setting is Middle America in the late 1970's and Lute (The Root), our hero, is a well-hung 18-year-old who has just finished high school and is vacationing with his family at their lake house. As a lead-in to this story, check out "The Root and His Aunt Barbara". And per usual, this is a work of fiction and all characters are consenting adults.
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After watching the threesome show of his mom with his Uncle Jack and Barbara, Luther crept to the backdoor of the lake house, entering quietly and as he slipped into Barbara's room. Knowing Barbara would be along soon, he lit a candle and then stripped down to his briefs before getting comfortable on the bed.
It wasn't long before Lute heard a tap on the door, and when it opened, it wasn't Barbara, as he had expected. It was his big sister, Bridget.
"Hello, Lute," Bridget said with a smile as she entered, "I thought I'd find you here."
"Hey, Bridge," he said, though unsure why she was there and what was going on, "What's up?"
"Not much. I just got home and thought I'd stop by for a bit," she said with a sly smile. "So, is Barbara still next door fucking mom and Uncle Jack?"
Stunned, Lute wasn't sure how to reply, so he fumbled around for a bit before answering, "Now wait, you know about what's going on with them too?"
"Yeah, I found out a couple of years ago."
"So you've known about mom and dad and Jack and Lynn for two years!" He asked in an incredulous voice, "Do they know that you know?"
"No, they still think none of us kids are on to them," she replied with a laugh, and then referring to their cousins, said, "And as far as I know, Tim and Jeff are still clueless."
"But Barbara knows that you know, right?" Lute asked, still trying to fit together the puzzle pieces of his confusing family.
"Yeah, Barbara and I've talked about it. Pretty wild, huh?"
"Damn straight, but why didn't you tell me?"
"I thought about it, but then I figured it was their deal, and that I should let them have their own private lives," she said, somewhat sheepishly, "Sorry, I know it's a shocker. But what the hell, it makes them happy, so who are we to judge, right?"
"I suppose," Lute said quietly while mulling over the whole situation again, "And from what I saw last night, it definitely makes them all happy."
"And you're now banging Barbara, right?" Bridget went on.
"Yeah, I guess I've joined our family's bed hopping association," he answered with a chuckle, "And what about you? Are you getting any family action?" He had asked this as a joke, so he was surprised by his sister's response.
"Well...I didn't just stop by Barbara's room for some deep intellectual conversation," she replied with her same sly laugh.
"Meaning what?" Lute asked, still trying to figure out what was going on.
"Meaning, Barbara and I have fun together sometimes too," she answered through a big grin.
"You and Barbara? Really?" he said with surprise, and then after a moment added, "Hey, you're not gay, right?"
"No, silly," she said as she pulled a pillow from a chair and tossed it at her brother, "But I do get nasty with girls sometimes. So I guess I'm technically bi-sexual, but I'm mostly just sexual - I love to fuck. And our Auntie Barbara is a great fuck, don't you think?"
Lute, moving closer to understanding what was really going on, replied "Yeah, no doubt about that," but then after giving it more thought said, "So, you came in here tonight to hook up with Barbara?"
"Kind of," she said, but then somewhat shyly she went on, "She told me you two had plans for tonight. And I, well...I was thinking maybe you'd be okay if I, uh, you know... watched."
Hearing this gave Lute pause. His sister was three years older and she was entering her senior year at a college in the city. She had stayed up there and worked the past two summers, so the two of them hadn't spent as much time together as they had in the past, and were less involved in each other's lives. Lute knew she had an active sex life - though he had been unaware that it also included women - but sex wasn't something they ever talked much about.
But he did know that his sister was intrigued with his big cock. That had become obvious after the second or third time she had "accidently" walked in on him in the bathroom they shared at home. She always apologized and rushed out, but not until she got a good look at her brother's thick ten-inch member.
So he considered her proposal while he quietly sized her up. Whereas Lute resembled their dad, Bridget was a younger version of their mother. She had her mom's same thick mane of dark wavy hair and pretty face, and a similar body shape - with the same set of great tits.
And just as she had found ways to get a gander at her his big cock, he had done the same by peeking in on his comely sister in various stages of undress when she didn't know he was around.
As these thoughts ran through his head, Bridget continued looking at her brother with a shy smile. But before Lute could frame a response, the bedroom door opened and in walked Barbara.
Freshly showered and wearing a light robe, Barbara regarded both Lute and Bridget and chuckled, "Hey, gang!" And then the 40 year-old vixen leaned over and gave Bridget a long sexy kiss before she slid onto the bed and did the same with Lute. Then snuggling up against him, Barbara smiled at the siblings and asked, "So, have you two discussed why you both happen to be here in your Auntie Barbara's room at this late hour?"
"We were just getting into that," Bridget replied, "And he's trying to decide how he feels about having his virtuous big sister watch him get naked and nasty with our sweet aunt." And then looking at her brother she added, "Is that a fair assessment of the situation?"
Smiling, he replied, "Yeah, that pretty much covers it."
After a pause, Barbara looked up at him and said, "Well stud, given the show that I just put on for you with your mom and uncle, it does seem like it's only fair to let your sister have a good seat for the next performance. I mean, it's not often that a girl gets to watch a young guy with a huge cock fuck a hot older woman. Right?"
Mulling this over as he chuckled and massaged Barbara's exposed thigh, Lute said, "I see your point," and then looking over at his sister who was still standing by the door, he said, "Sure, what the hell. Have a seat." And then he leaned over the bed and reached into the pocket of his shorts and pulled out a joint, lighting it with the candle on the bedside table. "But this requires some mood alteration, don't ya' think?" he asked as he took a hit and then handed the reefer to Barbara.
"Absolutely," she said as she took a long toke as Bridget sidled over for her turn.
And as the joint made a few more rounds, Bridget arranged a window fan to exit the smoke from the room.
They were all soon thrumming under the influence of the fine weed, and Bridget settled back into her chair by the window while Barbara and Lute began to kiss and caress.
"Mmm..." Barbara sighed as Lute slid his hand under her robe and began massaging her ass, "Your mom and Jack and I were just the warm up act, because you and I are gonna' be the night's featured performance, aren't we stud?"
"No doubt," Lute said quietly, still getting used to having his sister close by as his cock stretched his briefs.
"So don't be shy, lover, 'cause Bridget is just dying to see you fuck me with that monster cock of yours," she whispered as she slipped her hand into his shorts and began fondling his growing member. "And did she tell you that she and I get nasty sometimes, and that she loves to eat pussy?"
"Yeah, she sorta' mentioned that," Lute replied as he glanced over at his sister who now had one foot up on her chair, revealing the white panties she wore under her light sun dress.