Jessica explains everything.

Krista smiled over the campfire at her big sister. "So, are you guys at each others' throats yet?"

Jessica laughed. "Hardly; it's all sorted itself out. Sarah, John, and I are all getting along fine. How's the work on your Masters' coming?"

"I'm still trying to find a topic; what can I write in Behavioural Psychology that hasn't been done to ****?"

"How about 'Werewolfism as a psychological condition?'"

"What kind of stupid idea is that?"

"Hear me out. I said John, Sarah and I had an arrangement; well, this is it: he's the alpha male, she's the alpha female, and I'm the beta female. We're like a little wolf pack."

"Come on, that's crazy. You know the alpha male has sexual privileges with all the... Oh Em Gee! You're not!"

"I am. And it's fucking awesome! Sometimes its just the three of us, other times we invite other girls in."

"You know that's like, totally demeaning."

"No; Sarah makes the decisions; John goes along like a big puppy dog. I was creeped out at first, but after he fucked me the first time it all became clear. That's when I did some digging. He's got this antique leather penis ring–"

"Really?"

"Really. Anyway, Krista, it had a provenance, and I read it. The leather is made of wolf hide and was used by a cult leader who convinced his harem that he was a werewolf. The crazy part was that he and the women set up a wolf pack and anyone the leader fucked would start behaving like a she-wolf. The only real difference is that John lets his alpha female run the pack, and Sarah is doing a great job."

"And you're telling me this family perversion for a thesis idea?"

"Well, not just that..."

Jessica pulled her surprised sister in for a kiss; she tried to break away but their eldest sister Sarah, who'd been watching quietly from behind, grabbed her ass and pulled down her youngest sister's shorts. Krista struggled to no avail as Sarah's naked pussy pressed firmly into hers and started rubbing. Jessica shucked out of her bikini top and buried Krista's face in her cleavage.

"Welcome to the pack, little sister," said Sarah from behind, "John will be coming soon, not long after you do. I hope you like doggie-style."