"Dear Dr. Dirk!" Kyle said, and dropped to his knees to kiss the man's feet. The movement caused the loincloth to fail to one side, and Marcy sucked in her breath at the sight of the strong young cock in a state of throbbing erection.
"We have been heightening our sexual sensitivity with an extemporaneous playlet," Karla explained. "I am the cruel mistress, and Kyle is my worshipping slave. He crawls to me and begs permission to lap at my golden fountain as he revels in the pain from the whip."
Kyle's finger ran caressingly up the doctor's legs, and attempted to fondle his prick. "Perhaps our beloved experimenter would care to share our pleasure."
Villiers backed away, shaking his head. "No, not this time. I must observe and take notes."
Karla pouted, and Kyle's red mouth puckered up as though he were about to cry. Watching, Marcy thought how like children they were. Spoiled brats, really, who had been given so much all their lives that they couldn't stand being denied instant gratification of any desire.
Karla stamped her foot. "Why can't you be with us? You know we'd do anything for you! Why do you repay our devotion with indifference?"
"I repay it with scientific interest," Dr. Villiers said calmly. "I have brought the new experimental animal to you. I wish you to teach her the significance of troilistic lust, while I observe from the recording station."
Two pairs of eyes swung to Marcy, and she shivered slightly under their appraising stare. Would they accept or reject her? She didn't know which would be worse.
Karla's pout slowly turned into a sly smile, and her tiny red tongue flicked over her lower lip, while her free hand moved to her bare breast, and began fondling the extraordinarily large nipple.
Still kneeling, Kyle lifted his head, and his expression changed until it was almost an exact duplicate of his sister's. One of his hands moved just openly to erect his prick, and began stroking it.
"Yes, Doctor Dirk, we will be happy to teach your newest subject our games," Kyle said. "Won't we, Karla darling?"
"Oh, yes," Karla agreed enthusiastically. "And look, brother, they dressed her all up sexy for us."
"Her name is Marcy McCall, and her laboratory number is X-999," Dr. Villiers said. "Take good care of her, she cost a lot of money." He strode quickly to a door on the other side of the room, and went through it. Next to the door was what looked like a two-way mirror, and apertures through which cameras could be focused.
"Wait!" Marcy cried, starting after him. "Don't leave me!"
Kyle got to his feet and barred her way, putting an arm around her and holding her close. "He's not leaving us, really. He'll be watching everything we do, and if he gets excited enough, he'll come back and join us. Just relax, and let us teach you the things he wants you to learn."
Karla came up on Marcy's other side, still playing with her big, puckery nipple. "Shall we give her a quick kick to get her mind off Doctor Dirk? That outfit kind of turns me on anyway. Look how those lipsticked tits show through that thin silk. Doesn't that give you ideas?"
Without waiting for her brother to answer, she leaned forward and put her mouth right on Marcy's left breast, expelling her hot breath onto it as she wet it with her circling tongue. Kyle immediately did the same thing to the right breast. The sudden lustful assault caused Marcy to gasp, and her knees almost buckled.
"She digs that," Karla said, sucking noisily on the rigid flesh that gleamed like a ruby through the wet silk. "Keep sucking, Kyle. She's as hot as a pistol already."
The girl's hand darted up under the transparent outer garment, located the zipper, and opened the crotch of the tiny panties. Slipping a finger between the cunt lips, which were still swollen from the activities of the night before, she laughed gleefully. "She's all wet and slippery, and we've hardly touched her. Shall we just keep doing this until we make her cum? It shouldn't take long. Feel for yourself."
Marcy nearly fainted from excitement as Kyle's finger joined his sister's in her sopping cunt. And when both mouths returned to sucking greedily at her nipples through the sheer cover-up, tides of lust crashed through her, and she shook like a leaf in a gale. Two arms, one male and one female, went around her to support her, and two sets of fingers fucked in and out of her juicy furrow. Meanwhile two expert mouths licked and nibbled at her throbbing breasts.
"Wow! She's almost there," Kyle giggled. "Do her clit, Sis, and she'll go off like a firecracker!"
"Yes," Karla agreed, and the pad of her thumb made instant, tingling contact with the sensitive button.
"Oh God," Marcy wailed, jerking and pulling at the arms holding her, trying to get away from, or closer to – she didn't know which – the sucking mouths and probing fingers. She screamed again and fell to the floor, thrashing around wildly. Kyle and Karla fell with her, never stopping their maddening caresses, and obviously enjoying their control over her.
"Cum!" Kyle ordered, his fingers sinking into her passionate depths.
"Cum!" Karla echoed, her touch on the clitoris delicate but sure.
Marcy was lost. All semblance of reason fled, and she shook and trembled as though having a fit, wailing and rolling as orgasm after orgasm swept through her.
"Please," she begged helplessly, knowing she was at their mercy. "Please!"
And finally they relented and let her go.
"Great!" Kyle laughed. "The Doc has got himself a hot one here."
"He sure has," Karla agreed, busy pulling the filmy white garment over Marcy's head. "Now let's get down to some good, old-fashioned screwing. Dirk Villiers can call it an experiment if he wants to, but we all know what he wants to see is some plain and fancy fucky-fuck."
"Please, just go away and leave me alone," Marcy said, trying to crawl away from the reaching hands. "I'm going to take a bath, go to bed, and sleep for the rest of the day."
Karla grinned impishly. "Did you hear that, Kyle? Marcy wants to take a bath and go to bed."
"Groovy!" Kyle said, grabbing Marcy's ankle and hauling her back toward them. "That's just what we'll let her do."
"Sure we will!" Karla giggled. "We'll throw her in the Roman bath, soap her up, and show her what fun it is to play our version of bathtub games."
"And then we'll take her to bed and act out all the dirty jokes we've ever heard about the farmer's daughter," Kyle added.
"No," Marcy said, afraid of her own reactions as much as of this outrageous pair. Their all-pervading sensuality seemed to be catching. She could feel something dark and hidden stir inside her, responding to them. "I'm going to bed by myself."
"No you're not, baby," Karla whispered, bending over to kiss the sloping white shoulders and satin-skinned neck. "We've got all kinds, of things to teach you. Doctor's orders."
"What we did to you just now was only a sample," Kyle whispered in the other ear. "We're the only brother and sister sex team who admit to it openly. There isn't anything we won't do, especially for such a sexy, long-legged cunt as you."
Karma's soft little hands fluttered over Marcy's breasts, caressing them with feather-light touches. "You want us as much as we want you, Marcy. Look how hard and swollen your pretty titties are! You can't fool me. I'm a woman too, you know."
Marcy shook her head in denial of the girl's words, even though she knew they were true. The beautiful bodies so close to her were driving her crazy. The girl's perfumed fingers were gently pinching her nipples, and the youth's thumb was agitating her clitoris, while his palm pressed against the dripping cunt lips, moving in a deliberately arousing circular motion.
"Marcy is going to swing with us," Kyle murmured. "We've got her turned on, and we're not going to let her stop until she's done everything with us."
"Yes, she's all ours," Karla purred, unhooking Marcy's bra and tossing it aside. Her hands cupping the freed spheres, her lips sought Marcy's, and her honey-tipped tongue dipped into the other girl's mouth.