Dr. Sheldon Lee Cooper set the book down for the 5th time in the last 10 minutes. He didn't know what Penny and Leonard were thinking, giving him a book like this, but then again, he wasn't entirely sure why he had chosen to finally try to read it this morning.

No, he thought to himself, actually that wasn't true. He knew perfectly well why he had picked up that stupid book this stupid morning.

Sheldon got carefully off the bed, slipping his feet into his leather slippers as he did so. Taking off his purple plaid robe, he reached for the appropriate hanger and considered why he was doing what he had spent a whole 10 minutes trying to force himself to do. Oh right. Amy. It was because of Amy.

As he undressed, he carefully replayed over each and every comment and look from her, from their friends, from his family, and even from overly familiar waitresses on their date nights, that over the course of their relationship he had stored in his mind. There were simply too many. Or, more precisely, there were now fifty-two comments, both obscure and to the point, indicating things that were expected of him in this relationship, and more importantly, from Amy herself.

It was hard to ignore that many. Fifty-two, he thought, visualizing the number, smelling it in his nostrils like a living thing, the 6th Bell number. A decagonal number, just like twenty-seven, but an untouchable number, never the sum of any proper divisors of any number, never the answer to the equation x - φ(x). Never, Sheldon thought firmly, giving the book a dirty glare as he folded his PJs before placing them in the hamper. "I am untouchable," he said aloud, "I am fifty-two."

"You're thirty!" He heard Leonard bark at his doorway, footsteps padded with his athletic socks that would never be used in the pursuit of any athletics apparently carrying him out towards the kitchen.

"I'M FIFTY-TWO," Sheldon hollered back.

To which Leonard replied, his footsteps never slowing, "AND CRAZY!"

Sheldon sighed. He was not crazy. His mother had him tested.

He picked up his red Flash tee-shirt, the one with the white stripes around the sleeves, and the synapses in his brain immediately fired off a scene that he had replayed so often that the outlines of it seemed etched deep onto the back of his eyes. Her, the couch, that stupid monkey – he could remember how each wisp of smoke from the monkey's cigarette lazily circled behind her head. She had kissed him, and then, just like that, she had scurried away and gotten sick. But that he could erase – he could replay and rewind and fast-forward and rewind the moment over and over again whenever he wanted, and oftentimes when he didn't. The notion of using Kolinahr to suppress the memory came to him, but he decided not to. The flutter in his stomach was less than it had been originally, but it was still there, and it didn't make him feel bad. He put his arms through the sleeves of his shirt and shrugged his way into it, letting the scene play across his mind, and then rewinding it to play again.

Picking up his purple pants, Sheldon glanced at the book briefly, and then deliberately turned his back on it. The book really hadn't been remotely helpful to him; sex seemed both so simple and yet maddeningly complicated at the same time. Why did people bother with sex so much? Why did they care? It was the same practice over and over again – you lay down, things got hard, you placed it someplace, you came, and then it was over. Rinse, wash, repeat. Sex wasn't mechanically complicated. Sex was endlessly repetitive, and struck him as unbelievably tedious. Yet everyone around him obsessed about it constantly, was doing it constantly, and worst of all, after fifty-two comments, from Amy to Penny, from his mother's comments about Grandchildren to the Thai waitresses who noted sagely that their curry would spice up their blood for "a 5-star hot night," followed with a wink (Sheldon cringed at the memory of the wink), the outlines of his responsibilities as a man and as a boyfriend were becoming more clear.

Not that he cared, Sheldon reminded himself. None of this matters. Forget about it.

And he did.

He put on his shoes, lacing them up carefully, and then untying them and lacing them up again, and then once more for a third time just to make sure that it was done correctly. He tugged at the laces once, and then stood up, satisfied. He adjusted his sleeves, looking down at himself with a frown. When did they get so tight around his arms? He adjusted his pants, and tried to make a mental note to adjust his diet, but the note didn't want to stick. A lot of his usual worries and doubts weren't sticking the way they used to. Besides, it didn't matter. He and his body weren't really on speaking terms, and one day he'd be able to get rid of it entirely, becoming merely a brain and spinal cord merged into a robot body.

He picked up the harp strings he had purchased for Amy off his dresser and put them in his pocket. If he had been thinking about it, he would have noticed that his step became lighter, and that he had started to hum a tune she had played during their last boyfriend/girlfriend sing-along as he breezed out the door of his bedroom, said goodbye to Leonard, and grabbed his jacket. However, Sheldon had other things on his mind now. He was off to see Amy and muscle memory would lead his steps there, and he was thinking about the first thing he would do as a robot. Or with a skeleton fused with adamantium. Or what if his consciousness was fused with a train? Trains, train shop, locomotion, motion: velocity, acceleration, displacement and time – and off his mind sped, down a million theoretical tracks, until he was surprised to find himself already at her door.

Knock, knock, knock, Amy – rinse, wash, repeat. Three times he would knock then say her name, three times three was nine, times three again, twenty-seven, another decagonal number, and in his mind 27 perfect lines assembled to form a perfect, smooth cubic surface, and then the aliquot sequence fired off in his mind – 27, 13, 1, 0 – each number it's own shape, its own taste, its own texture, its own personality, blending together to form the perfect cube, and Sheldon was satisfied that he was square with the world.

He waited, tilting up on his tiptoes with eagerness, and in the next split second she opened the door and let him in.

Sheldon drank his glass of Yoohoo as Amy carefully unwrapped and laid out the harp strings on her coffee table, explaining that the red was the "C" string and the blue the "F," and he listened with only half his attention on her words, as these were things he already knew. Instead, he noted that she was wearing her usual stripped cardigan, that her voice as alert and so utterly sensible, and the way her graceful hands carefully spaced each string exactly a centimeter apart. In fact, she was using a ruler to measure the spaces between them precisely, but she had missed one and he reached out to correct it. She quickly smacked his hand away, hard, scolding, "Sheldon! I'll get to that."

"Ow!" Sheldon said, jerking his hand back and cradling it to his chest. That hurt. He looked at it, inspecting carefully, then thrust it out to her accusingly, "Look, it's turning red."

Amy swayed a little, frowning, her expression indicating she was properly chastised. "I'm sorry, Sheldon," she said, looking at the red mark. "You know how I am about my harp strings." She looked at it more closely, and then asked, "Does this constitute a booboo or ouchie?"

He thought about it, and then decided, "Yes. It does."

Amy got to her feet, going to the kitchen and opening the door to her freezer. As she got out some ice, and started to wrap it up in a towel, she recited the terms of the Relationship Agreement. "Section Four, Booboos and Ouchies," she said, "When the boyfriend sustains a booboo or ouchie, it shall be the responsibility of the girlfriend to tend to the wound in a timely, expedient manner, applying those techniques as outlined by the American Red Cross, with tools or items that have been properly sterilized or washed thoroughly beforehand."

Amy knelt next to Sheldon, and pressed the ice to the back of his hand gently. A jolt like lightning hit his spine, and his body broke out in goosebumps all over. An absolutely normal response to a cold towel being compressed to his flesh, he thought, though he couldn't quite figure out why his heart had started racing. He stared at the pale hands holding and covering his own, and then at the glossy brown back of Amy's head.

She went on, "The girlfriend shall also – Sheldon?" She pushed back the red sleeve of his long tee-shirt in a way that stirred the hair of his arms in such a way that another jolt went through him. "You seem to have developed a case of cutis anserine," she said, using the medical term for his goose bumps. She looked up at him and noted seriously, "If you were a porcupine, your quills would be quivering. Quivering like a properly struck harp string." Then she flashed the quickest of smiles at him, delighted with her own cleverness, and Sheldon felt himself melt in that weird way he did sometimes in her company, and he found himself just staring back into her green eyes and tilting his head slowly.

Why did it please him to see a blush spreading over her cheeks? Or the way she swayed slightly, with that lopsided smile of hers, when she looked away? Her hands flexed and tightened a little around his, flattening out the ice against his skin, holding it tighter, and Dr. Sheldon Lee Cooper found himself staring and unable to look away. Finally, she looked back at him, still smiling oddly to herself, and her gaze turned slowly from shy to curious, and then to penetrating. Her eyes flickered across the features of his face, and Sheldon tilted his head to the side again, that jolt of electricity hitting him at the base of his spine for the third time.

Three, Sheldon thought, The first odd prime, the first lucky prime, the first unique prime. She is odd, she is three. I am three, I am lucky. We are three, we are unique, we are perfect.

"I've had about enough of this," Amy said, and Sheldon didn't have time to think about what she was talking about. Her lips were on his, in hot contrast to the rest of his cold body, and all of his thoughts flew out of his head like they had been ordered away by a particularly bossy breeze. His eyes closed, and when she was done kissing him, he opened them, but she told him to close them again, and he obeyed.

"What are you doing?" Sheldon asked, feeling something soft, like cashmere, being tied across his eyes. She had taken the ice away, and he touched one hand to the back of the other, feeling that cold and numb spot on his skin. His whole body was tingling from the top of his head to his toes, and yet he didn't feel scared, and he didn't feel like fighting it. A knot was being tied firmly at the back of his head.

"An experiment," Amy answered calmly, and Sheldon decided to wait and see what that meant. Every inch of him wanted to know what she meant.

Somehow he could tell she wasn't close by. He heard the sound of the loose harp strings rustling faintly as she picked them up from the coffee table. He heard the sound of the harp being stroked once, and imagined her hand caressing it in one fluid motion as she walked by it, moving behind him somewhere.

"Sheldon," Amy said, sounding as centered and controlled as usual, "You trust me, don't you?"

"Yes," Sheldon answered, unwaveringly. He did. Completely.

"Then let me be in control for awhile." Sheldon shifted his weight, a complex range of emotions going through him at this request, but eventually he calmed and managed to nod his head in agreement.

He felt her touch on his cheek, caressing gently like a reward for his acceptance. She was behind him, and her hand traveled more firmly down his back, joined by her other, and they began seek out knots and muscles, pressing and circling firmly, making him jerk and gasp out loud. She was speaking, naming off the muscles and tendons as she touched them, playing them with her fingertips as deftly as she played the strings of the harp, but Sheldon wasn't exactly following. If there was any fight or resistance in his body at all, if he had any reservations about letting her take control of him, the pressure of her fingertips between his shoulder blades pushed them away, and the trail of her thumbnail down his spine banished them, sent them scurrying away on each delicious shiver to a place of oblivion. He rested his elbows on his knees and buried his face deep into his hands, shivering and weak by the time she was done.

He felt her hand take his upper arm and pull it back behind him, and then the other. He lifted his head blindly, and said nothing until he felt his arms being bound together by thin wire. He opened his mouth to protest, but she beat him to it.

"The strings are thin, Sheldon," she said, her voice different this time. Lower, and huskier, but still controlled. "If you fight they'll dig deep into your flesh and leave marks, so don't squirm. Don't move at all." She paused, and Sheldon felt the strings lashing over his tee-shirt just below the elbow, and being slowly crisscrossed and tied all the way down to his wrists. "Take a deep breath while counting to seven," Amy said, "And count to four, holding it in, and then let it out, counting to seven."

Sheldon counted, and waited. "Breathe again," she said, and he did, continuing to count. Four times seven was 28, a harmonic divisor number, a happy number, the second perfect number, times seven again was 196, a powerful number and a practical number. He breathed in and held it, harmonic, happy, perfect, and breathed out again, powerful and practical. Seven, an odd number, four, an even number, seven, an odd number. Odd, even, odd, even, happy, powerful, perfect, practical - it all pulsated in his breath. Odd, even, odd, even - harmonic, in sync. He shifted just slightly, testing the strength of the harp strings against his skin, felt them hold him firmly. He breathed to Amy's count again, his heart thumping harmonically: even, odd, even, odd.

He could do this.

For a long time it was quiet in the apartment, and all he heard was soft rustling of cloth, the sound of his own breathing, the far away rush of traffic and city from her window. Everything felt light and hot, as if he was standing in the sunshine.

Eventually, he felt a hand on his chest, and he was being pushed backwards into the depths of the couch with his arms pinned behind him. He felt her weight and warmth settle on his knees, and then her hips push inwards against his, nestling there. He felt her body press into his, her chest against his, and a sensation sharply hardening between his legs and starting to throb almost painfully.

Her hands, cool and smooth, caught his face and tilted it upwards, and then her lips found his again, and he submitted to her kiss.