Penny resumed her circulating, but her mind was spinning. Sheldon and Leslie? Really? Her head tried to convince her that the glance he had thrown her had been nothing, but it couldn't. She watched Sheldon as those of her friends who didn't know him tried to make small talk; how he would start waffling about string theory and they would tune out and his eyes would flit back to Leslie and Leonard. She tried to work out the look he was giving her. It certainly wasn't lust; resentment, possibly? But not of her being with Leonard, that was obvious. Was he resentful that she was still in his life? What had happened? How bad had things been between them? She thought back over all the swipes they took at each other, all the snide comments about research and theories that she now realised were clearly hiding something deeper. Something he had been trying to forget.

She figured that answered the question of why he had never told Leonard, anyway. Whether he should have, however, was another matter. For a man who couldn't keep anyone else's secrets, she thought, he certainly seemed capable of keeping plenty of his own. She would definitely need to do some more digging.

The party eventually died out about 2am as she finally managed to wave off the guy who had been flirting with her all night. Tonight, she just hadn't been interested. Leonard had left with Leslie an hour ago, and she didn't have a clue where Howard and Raj had gone. She did, however, know exactly where Sheldon was. She surveyed the wreck of her apartment, smiling when her eyes came to rest on one of the greatest minds of the 21st century, curled up on her couch in his Batman outfit. He had his cape wrapped around him. She decided to leave him be and fell onto the bed, head spinning gently from alcohol and revelations.

She had just managed to drift off when she heard a noise from the lounge. Crap, Sheldon must be up. Now she'd be getting a lecture for letting him fall asleep on the couch. There was a clattering noise and she pushed open the bedroom door. The Caped Crusader was washing up.

"Sheldon, sweetie? What are you doing?"

"Oh, Penny. You're up. I'm afraid I couldn't allow you to sleep in the vicinity of this mess. You – and by association, me - are at risk from airborne mold spores."

Well he wasn't slurring his words, so the sleep had apparently had some sobering effect. Almost as soon as she thought that, a plate slipped from his grasp and shattered on the floor. She winced at the noise. Sheldon looked at the smashed plate as though it was something worthy of inspection. "Fascinating. Evidently my psychomotor skills have not completely recovered from the effects of the alcohol yet."

"Ok, Sheldon, sit down." Coffee was clearly required, since he wouldn't sleep until he'd cleaned and he couldn't clean until he was sober. He looked like he was going to protest, but then caught the look in her eye and thought better of it. He sat meekly on the sofa while she cleared up the plate fragments and brought him the drink, obediently taking a few sips.

She sat down next to him. "Ok?" Sheldon nodded. "Sooo…did you actually enjoy any of tonight?" she smiled at him. He frowned as he considered the question. "I believe 'enjoyed' would be a little strong, but it was …tolerable. Certainly I am beginning to get used to the strange looks your friends always seem to give me." He looked up at her from under dark lashes.

"Aww, sweetie." She felt a twinge in her chest. "They don't mean anything by it… they just don't know you like I do." Sheldon listened, then did something she wasn't expecting; he smiled softly at her. "I appreciate your sentiment, Penny. But I believe that if I spent enough time with them that they indeed 'got to know me' then they would still not see me as you do."

She suddenly felt exposed. "How do I see you, Sheldon?"

"Well, your previous statements would indicate you at least consider me a friend. I doubt the majority of the people here tonight would be interested in maintaining a friendship with me. I appreciate it is sometimes…difficult."

Penny nearly fell of the couch. Sheldon Cooper, admitting he was…'difficult'. The coffee didn't appear to be working yet and she briefly considered taking it off him before he could sober up. She was working on an idea of how to keep him permanently half-tanked when he interrupted her thoughts.

"Penny…why were you so interested in my previous sexual encounters?" She looked up and suddenly his eyes were burning into hers. She tried to think of an answer that wouldn't make her sound, well…jealous. She decided to go with an edited version of the truth.

"Um. I'm not actually sure. I think it was just because it's you, and you don't ever seem interested in women. So it was a shock to find out that maybe you had been once…" She debated with herself, then decided to just say it. "I know it was Leslie."

She had expected him to be shocked at having been figured out, but he just accepted it with a look of resignation.

"I had wondered when you would figure it out. You did so more quickly than I anticipated; your powers of observation when it comes to social nuances are clearly highly developed."

"Sheldon…was that a compliment?"

He raised an eyebrow. "No. It was an observation."

She sighed. "So are you gonna fill me in as to how you two ended up as arch enemies? You might as well, since I know this much already." The compulsive need to know had been fighting her desire to forget all about the idea of Sheldon and another woman. As usually happened, she had decided to go with the plan that would probably involve her heart getting battered against a wall.

He pulled his cape around him tightly. "Very well. But you must agree to keep this between ourselves and also, not to laugh." He flushed slightly.

"I promise, sweetie." She couldn't promise not to get freaked out half way through and stick her fingers in her ears though, she added silently.

He looked at her dubiously, but continued.

"When I first moved to California to work at Caltech, I did not know Leonard and no one had replied to my advert for a housemate as yet. Very soon after I arrived there was a social function in which we were expected to 'shmooze' for grant money. I attempted to make my excuses but was informed that my contract could be rescinded very easily should I fail to meet the obligations placed on me by my role. So I attended. Obviously, this was an uncomfortable situation for me and I succumbed to the lure of free alcohol. At some point during the night I recall being accosted by Leslie Winkle, and we somehow ended up at my apartment. My memories of these initial interactions are very vague. Looking back on the circumstances however, I believe she was using me as some form of 'stress release'; certainly she seemed somewhat...single-minded in her pursuit of coitus. In any event, the situation was not ideal. There were problems from the outset, which of course I attribute to the alcohol."

Penny had to act fast to stop the little smile that wanted to dance across her lips. Of course; with men, it was always the alcohol. He continued:

"Apparently I did not perform as expected. The whole thing was over very quickly, and not in a particularly pleasurable sense. I believe she became frustrated and took it as being a personal slight, and I must admit I was not sufficiently well versed in post coital etiquette as to be able to convince her otherwise. In fact, I believe I may have made the situation worse, judging by her anger and subsequent verbal abuse."

Penny looked blank for a second as she translated the speech in her head.

"So you're saying you got really drunk, she seduced you, then you couldn't keep it up and she took the huff…? And then you opened your mouth and somehow made it worse?"

"Apparently I may have said something to insinuate that she was insufficiently attractive to overcome the problems inflicted on me by the alcohol. I don't really remember…"

"…because you were drunk, I get it. Ouch. No wonder she hates you!" Sheldon scowled at her. She ignored him. Something was bothering her about the scenario. "Sheldon, I get what you're saying, but I just can't imagine you getting drunk and hooking up with someone you hardly knew. I mean, why did you go along with it?"

He looked embarrassed. "I was at a party full of people I did not know, alone in a new city. I do not like change at the best of times, as you know, and this situation left me feeling…vulnerable. Leslie offered the potential for emotional support at the time. Or so I believed."

Penny felt a pit open in her stomach. Sheldon had felt vulnerable? That was something she couldn't imagine. At the same time as feeling sorry for him though, she couldn't deny the rush of relief that ran through her at hearing the story. She breathed out slowly. It had meant nothing to him. She didn't want to admit to herself how much that meant to her. She felt an overwhelming urge to giggle, but the look on Sheldon's face persuaded her that would be a very bad idea.

"Well. Thank you for telling me, Sheldon. It means a lot to me that you would trust me with something like this." Something else suddenly occurred to her.

"But…Sheldon, why did you even mention this to me in the first place? You must have known I wouldn't let it lie. Unless…." He was watching her closely as she spoke slowly, thinking aloud. "Unless you wanted me to know. But why would you do that?"

He was giving her that look again, the one that suggested he was evaluating her potential responses to what he was contemplating saying.

"I admit, I had an ulterior motive in piquing your interest thus. You said yourself, I'm not interested in women. And that's true, I'm not. But for reasons I'm not entirely sure of, I'm interested in you, Penny. I am conscious that people do not consider me as being part of the potential mating 'pool' as you will, but for some unfathomable reason I wanted you to be able to see me…differently." He couldn't meet her eyes. "Unfortunately, when it came to actually discussing it, it was more difficult than I anticipated."

Penny was starting to feel like the whole evening had been one long, really weird dream, and this last revelation – that Sheldon was interested in her, whatever he meant by that – was doing nothing to bring her back to reality.

"Wait, you're…interested in me? Sheldon, what are you saying? Interested in the way men and women are interested in each other? Or as in the way you might be interested in a new kinda bacteria or something?"

He finally met her eyes. She thought she saw a challenge in them. "You're the expert in social behaviour here, Penny. What do you think?"

She thought lots of things. She thought of how they were complete polar opposites, how they fought like cat and dog, how utterly infuriating he could be. She thought of how he tested her, challenged her more than anyone else she had ever met, how she had learnt so much from him. She thought of how sweet he could be, how his casual comments about her attractiveness meant so much because he had no hidden agenda. She thought of how cute he looked in the cape and wondered when his knee had started pressing against hers. She thought of how amazing it felt when he smiled at her.

She thought of how she had felt over the last two weeks, imagining him with another woman.

She thought of how she felt now, his eyes boring into her.

She dredged a phrase from her memory.

"I think…I think your methodology was flawed, Sheldon. You can't judge something as complex as sex on one bad experience." He raised a single enquiring eyebrow, and she met his eyes with her own challenge. "I think you need to repeat your experiment."

He swallowed hard before he replied, and she was briefly transfixed by that bobbing adams apple. She fought the urge to kiss it. His voice was hoarse.

"You present a fascinating supposition. Would you perhaps be interested in assisting me in the experiment?"

Almost before he had finished she was on top of him, cupping his face and pressing her mouth against his. She was pretty sure the alcohol was responsible for the fact that he kissed her back without first insisting she rinse with an antibacterial mouthwash. She was also praying the alcohol wouldn't be affecting any areas other than his brain, but from what she was feeling as she ground against him that didn't seem like it was going to be an issue. Although…

"Sheldon?"

He looked at her enquiringly.

"I have to ask…is that a batgrenade on your utility belt or are you just pleased to see me?" she deadpanned. He frowned, and she giggled, euphoric with the strangeness of the situation.

"I do not understand the question…" She silenced him with another kiss, slipping her tongue into his mouth as he made a surprised little noise.

His hands started on her hips before wandering down to her thighs in search of flesh, denied as they had been by the fabric of her dress. She had come dressed as Alice, and as she snuck a glance at the man beneath her the thought occurred that she was well and truly through the looking-glass tonight. Then Sheldon's hands were sliding under her skirt and she stopped thinking anything for a while.

Afterwards they lay together on the bed, Penny dozing whilst Sheldon analysed. After the experiment on the couch had proven successful, he had proposed altering the location variable to thoroughly test the reliability of their findings. It would appear that having successful coitus did actually increase the desire to achieve it more regularly. Hm. He wondered if there was a research paper in there somewhere. He briefly debated informing Leslie of his findings, then rejected the idea as some ancient instinct for self-preservation kicked in. He had a brief moment of self-doubt as he considered whether any of his other theories were untenable, but promptly rejected the notion. This was clearly an unfortunate aberration.

Although, he had to admit as he watched Penny sleep, he was quite happy to have his initial hypothesis disproved…just this once.

Penny heard Sheldon shuffle next to her, and then smiled to herself as his hand hovered uncertainly above her before gently coming to rest on her hip. Images of the last few hours floated through her head, and her final hazy thought before drifting into a contented sleep was just how fun science could be, when you had someone to experiment with...