Disclaimer: I own nothing, though I wish I had my own Sheldon.

This is just a little idea that popped into my head, while watching The Dead Hooker Juxtaposition. At the end when they are all sitting eating Sheldon is annoyed thinking their new neighbour is jumping on her bed when they all hear the creak of bed springs…. He apparently really is that innocent!

Meanwhile I am desperately trying to finish my other on-going Shenny work, 'A Pair'. I've written and re-written the next chapter around five times. I'm seriously stuck with it, so if anyone has any ideas of what they'd like to see happen, feel free to review or PM me.

I hope you like this one-shot. Please review

The Chemistry Hypothesis

'Penny..' Sheldon interrupted in a strange voice, bringing their shouting match to an abrupt halt.

'What?' she hissed, her face flushed with anger and annoyance.

They had been arguing again. This time it had spawned after he had accused her of hiding his Flash Ultimate Hero mint condition limited figurine; all supposedly in response to him posting a cleaning schedule on her front door along with a roll of bio-hazard tape.

Penny had been less than impressed with the implications.

He looked perplexed as he stared down at her, his hand resting lightly on his stomach.

'I feel funny' he gestured to his stomach, 'here'.

'Did you eat something bad?' Penny sighed, aggravated.

'No' he shook his head in his childlike way, 'this isn't an isolated instance. I've noticed it before. But it only happens when I argue with you'.

He looked at her accusingly as he spoke, obviously itching to blame her for something.

Penny looked up at Sheldon for a moment, attempting to choose her words carefully, while consciously biting her tongue on her anger. She knew exactly what it was but she was certain he wouldn't either like or understand.

'What is it?' he demanded, seemingly sure she would know the answer.

Penny opened her mouth, then shut it, then opened it again, each time changing her mind.

'It's called chemistry' she said finally, her cheeks pinking slightly in annoyance.

'Penny' he replied condescendingly, 'as a theoretical physicist I have dabbled in the uncomplicated art of the chemistry sciences and I assure your unskilled mind that this feeling is not a result of chemistry. Although, now I consider it, it may be due to airborne pathogens that are transmitted during our verbal sparring'

As he considered the implications of his words he sprung back, pulling his top up over his mouth and nose.

'Leave' came the muffled command as he pointed to his front door.

'Urgh' Penny let out an un-ladylike groan in response.

'I didn't mean sciencey chemistry you nutcase' she huffed, moving forward and tugging his top down off his mouth, 'I meant the chemistry you get between people'.

His head tilted to the side as he considered her hypothesis, before dismissing it.

'Society induced hokum'.

'Tell that to Scarlett Johansson and Jeremy Renner' Penny muttered under her breath in response, admitting that for once she had actually enjoyed one of the films they had dragged her to see.

'More of your friends?' Sheldon questioned baffled.

'What? No!'

'Right, I swear on my mother's life I didn't take your toy and so help me if you stick another note on my door about cleaning I will get Howard to send a message to everyone you work with telling them to call you Moonpie forever. Clear?'

'I wouldn't be forced into acting if you were more diligent with your household chores' he countered, before adding quickly, 'but I will not post anymore schedules on your door'.

He looked nervously over at her threatening face.

'I still do not fully grasp the concept of human 'chemistry'?' Sheldon asked ashen faced, with a hint of curiosity, 'what is its ultimate goal?'

'Are you seriously asking me that question Sheldon?'

'I am always serious' his naive reply making Penny realise just how little that boy knew about the real world.

'Oh, bugger it all to hell!' she exclaimed loudly to Sheldon's surprise.

Moving over to him in three long strides she grabbed the back of his head with both hands. Tugging him down to her level and bringing her body flush against his, she paused.

'This is chemistry' she said, her lips millimetres from his. She did not allow their lips to touch but she made sure they could feel each other's hot breath.

His eyes widened in alarm and he wilfully tried to pull away, but her grip held him firmly in place.

'How do you feel now Sheldon?' she whispered her voice huskier than she had intended.

If possible his eyes widened further and Penny finally took pity on him. Releasing his poker straight body she stepped away, smirked at him and then walked out of the apartment happy she had won the argument.

XoX

When Penny came home from work late that night she found another note cello-taped to her door.

'Chemistry (noun) – the spontaneous reaction of two people to each other, comprising of a mutual sense of attraction and/or understanding'.

It was typed as opposed to hand written and she was still staring at the words when Howard and Leonard came out of 4a.

'We have been wondering who put that on your door all evening' Leonard commented as they all stood staring at the definition.

'A4 sheet, non-laminated, typed' Howard reviewed in his typically scary way, 'doesn't bare all the hallmarks of a stalker, but it's a close call'

'I haven't got a stalker Howard'.

'Fair maiden, the question is why wouldn't you have a stalker?' he leered, adjusting his tight red trousers.

She growled at Howard in response and he had the good sense to back away slowly, leaving Leonard and her alone in the hallway.

'You don't have a stalker do you Penny?' he asked unsurely, a hint of jealously sneaking into his tone.

'No!' Penny exclaimed, carefully pulling the note off the door and slipping her keys into the lock.

'Will you be coming over for dinner?' he asked hopefully to her back as she let herself into her apartment.

'Sure' was the distracted reply, 'be over in a bit'.

'Well that was weird' Leonard said the empty hall as the door closed in front of him. He was left with the image of Penny standing at her kitchen island staring down at the piece of paper, a strange look on her face.

'Will Penny be joining us for dinner?' Sheldon asked when Leonard came back into the apartment.

He looked up questioningly from where he was perusing the take-away menu.

'Yeh. She didn't seem to know who left the note either'.

Walking over to their fridge he didn't notice the nervous ticks that blossomed over Sheldon's face, before they were quickly supressed.

Before long the whole gang were sat round the living room eating Chinese; Sheldon in his usual spot, Amy alongside and then Howard, Bernadette, Raj and Leonard in various spots around the table. Unlike the OCD member of the group no one was much bothered where they sat.

The evening was all going all fairly pleasantly until Penny came in.

'Amy' Sheldon spoke up at Penny's arrival 'you're in Penny's spot'.

Penny stared at Sheldon in shock for a moment before quickly reassuring Amy that she didn't have to move. Taking her dinner from Leonard who had picked it up for her, she settled down crossed legged on the floor.

'Penny, you are not sitting in the correct seat' Sheldon persevered, 'your seat is next to me'.

'Sheldon' Penny huffed, slamming her glass down on the table in irritation, causing him to flinch perceptively, 'for the last time. Amy is already sitting next to you. I am not gonna make her move just to keep your crazy at bay'

The group were looking between the two in varying levels of interest and discomfort.

'Come on guys, it doesn't really matter' Leonard attempted to pacify, though he quietened quickly when he received a glare from each of them.

'Penny I am not adverse to moving seats. I fully comprehend why anyone would prefer to sit by you' Amy interrupted, the only hint to her hurt was the small wobble in her voice over the word 'prefer'.

Penny took one look at the pain in Amy's eyes before rising to her feet and throwing her dinner down on the table.

'You are an arse Sheldon Lee Cooper'.

Storming out of the apartment she only just caught Howard's words.

'I could have told her that five years ago'.

XoX

Penny was annoyed, sober and hungry. Never a good combination.

She had been banking on Leonard buying her dinner. There wasn't even a pack of dried noodles in her cupboard. She had taken all the tips she had earned that evening straight to the bank to pay her rent. To say she was flat broke would have been a laughable understatement.

If she wasn't so close to tears she would have laughed. Once again Sheldon ruined an evening by insisting on starting an argument with her. Surely he would have known that she would not have done what he'd demanded. He'd been looking for a fight she realised.

He really was an arse.

She barely had to think as she rooted through her cupboards for the one thing she knew she did have. She breathed a sigh of relief as she poured herself the first glass of whiskey. Downing it in one did nothing to relieve the hunger pains. Pouring another she walked round her kitchen island, before changing her mind and going back for the bottle.

Settling on her couch, swilling the amber liquid round in the glass, she couldn't even be bothered to reach for the remote and turn on her tv set.

The more she drunk the more she thought about the hunger in her stomach and the look on pain on Amy's face.

She was well on her way to being drunk when she pulled herself off the couch, the feeling of pent up rage begging to be released.

Storming over to 4a she didn't bother to knock, pushing open the door so fast it banged on its hinges. The noise caused Sheldon to jump up physically from his desk in fright.

'What is the meaning of this?' he exclaimed when he finally found his voice, his hand still pressed to his chest above his heart.

'You Sheldon are an arse' she said accusingly, the slur in her voice only too evident.

'I believe you have already informed me such' his face dropping into a scowl.

'Well' Penny exclaimed, 'I'm telling you again. So you can get it into that thick geeky head of yours that you are the rudest, coldest man I have ever met. Didn't you see the look on Amy's face! You're unbelievable. I don't know why I put up with you!'

'Are you quite finished?'

'No' Penny snorted disdainfully, 'You have absolutely no idea what you're doing to her, do you? You think that you can just…'

She paused in her rant when he stepped towards her.

'What the hell are you doing?' she hissed as he took another step towards her. She backed up further and further until her back hit the door.

'Chemistry, you said' came his quiet murmur. He looked distracted; as if he hadn't been listening to her rant at all, his mind on other things.

Stepping closer still, his hand came up to rest unsurely above her, pressing his palm flat against the door. He was looking at her like she was an equation to be solved, a problem to be fixed, a blight in his otherwise ordered existence.

'Chemistry' he murmured again. Leaning down he repeated the action she had bestowed unwillingly on him only 12 hours before.

He hovered in front of her, their lips only breaths apart. When she had told him that they had chemistry she had meant it. She had always felt it. It was just one of those things that she had begun to think of hand in hand with their arguing. The feeling in her chest was just another part of the anger.

She knew he had felt it too, only he had never been able to place what the feeling was till she had told him.

Stupid, stupid girl, she berated herself.

His breath was hot and he had closed his eyes. Up close she could see every freckle on his nose, every delicate eyelash. It was rare for him to be so close and so very quiet.

She had to use all of her strength to push him away; he had always been so much larger than her. In doing so she lost her balance, the alcohol in her body messing with her, and he lunged forward to catch her on some built-in gentlemanly instinct.

The hands that had caught her waist sprung back to his side in a moment as if she had burned him and Penny stared openly at him, struggling to remember why she had come here in the first place.

Reaching for the door handle she quickly fled. After she shut and slid the deadbolt across on her own front door she glared over at the half empty bottle of whiskey.

It was the alcohol's fault she decided, definitely the whiskey's fault. It had been the words she had chanted to herself many times before. When in doubt, blame the alcohol.

XoX

The next time she saw him was the following evening at the Cheesecake Factory. It was a rare sight nowadays to see the just the four boys sitting at their usual table.

'Hi Penny' chimed Leonard, happy as always to see his girlfriend. Howard greeted her in his usual creepy way and Raj smiled goofily at her, mute as always. Sheldon, however, stared resolutely down at his menu and didn't acknowledge her presence.

Well, if he was gonna play that game, she thought stubbornly.

Amy had called her that morning, complaining about her resistant boyfriend. Nothing new there then, but this time Penny had caught an undercurrent of something else. She had mentioned more than once that it was only natural that a man would choose Penny over her.

It made Penny angry. Awkward, uncomfortable and overly familiar that Amy was, she was the first friend Penny could say didn't have a hidden agenda. When Penny had been at school she had been a cheerleader. She had been one of the most popular girls in school and had hung with the popular crowd. She had hated it.

She was now ashamed to admit that she had been one of the girls that would have picked on Amy's type. Being friends with Amy had started with a sense of penance, then, she had actually started to like her in a weird kind of way.

Now, her friend had been hurt by the man hiding behind his menu in front of her.

'So, Sheldon, I was looking around on the internet this morning. How much do you think I could sell a Flash doll for?'

'Well that would depend on the type' he answered immediately, looking up at her, 'and the condition of the figure and of course on which…'

'Wait!' he interrupted himself suddenly, 'why would you have access to a Flash figurine?'

He looked a little wild for a moment, his eyes wide in alarm.

She only smirked, said nothing and turned to her boyfriend and remaining friends to take their orders.

She could feel his eyes burning into her as she walked away. Ringing up their order on the till she weaved around with the ease of an experienced waitress picking up the drinks tray, menus for another table and a spare fork for a customer she had just seen drop their own.

This shift had really been dragging and she was just quickly slipping outside for a breath of air when she was abruptly dragged sideways into the dry foods store cupboard.

'What the!' she cried out, turning, ready to go all kinds of Nebraska on the idiot who had grabbed her when she saw who it was.

'Sheldon! What the hell do you think you are doing?'

'I demand you return my possession' he growled in a tone she knew was reserved for when he was furious with her.

'I haven't got your damn doll' Penny hissed poking her finger into his chest, 'I was messing with you. I'm just so angry, you nutcase. I had your girlfriend on the phone for an hour this morning all because you are too stupid to see when you make her upset. You're in a relationship Sheldon, try acting like it'

'Me!' he replied in shock and equal anger, 'you always sit next to me on the couch. I see no reason why that should change just because Amy Farrah-Fowler and I have classified ourselves in a heterosexual association. She understands.'

'You really have no idea do you' Penny was struggling to keep her voice low, the door to the store cupboard may have been closed but she knew how thin the walls in this place were. The whole restaurant could probably hear their argument.

Stepping into his personal space once again she poked his chest harder, punctuating each word.

'Amy is delicate. You have to be gentle with her'.

He was silent after her words and it was only then that she became aware of how hard they both were breathing.

'Your eyes are dilated' he said suddenly.

'So?' she said with equal distraction.

'Chemistry' he whispered again before he did something so out of character that Penny's heart jumped.

He lunged forward, fast, so much so that her back hit the metal shelves behind her painfully.

Without seeming to think his lips crashed down on hers. It was rough and messy and once she recovered enough she realised that she was kissing him back. It was more than reciprocation though. It was a battle. She fought for dominance, her lips clashing with his. Her hands reached up, at first to push him away and then moments later she dragged him closer.

He was sloppy and inexperienced but it wasn't stopping him. It wasn't stopping her either.

She quickly deepened the kiss, slipping her soft tongue into his mouth. He moaned desperately at the sensation and pressed closer to her. His hands which seemed to be moving of their own violation slipped round and tugged a fistful of Cheesecake Factory uniform towards him.

With their bodies flush together there was no mistaking either of the reactions to each other's passion.

'Oh!' came a yelp that broke them apart suddenly as light spilled into the cupboard. Breaking away with a shove, Penny met the eyes of one of the kitchen boys that stood frozen at the door.

'Scat' she barked in embarrassment.

They were quiet for one long moment, breathing heavily, their lips swollen, clothes rumpled and hair mussed.

'Shit' Penny hissed before chancing a look at the shell shocked expression on Sheldon's face. She swore again before legging it.

XoX

She saw his shadow beneath her door long before he knocked.

She had to get this over and done with, she knew that. The days that had passed since then had been awkward and Leonard had started to notice something was up. She had cheated, he had cheated. In another life they probably would have been an awesome couple.

Swinging the door open, his fist was held high as if he had been just about to knock and hadn't been stood there for five minutes.

'It never happened' she snapped before he had a chance to speak.

'You have Amy, and I have Leonard. It never happened. End of'.

He was silent for a moment. His ice-blue eyes seemed to look straight through her and it hurt.

'I think that would be the best course of action' he said finally, 'will you be joining us for dinner?'

Nodding, she closed her door behind her and followed him across the hall. The guys were all there, including Amy and Bernadette.

'See, I told you Sheldon would have the persuasive technique to ensure our sunny friend would join us' Amy smiled serenely.

They all looked up at her words, expecting Sheldon to go ape-shit and demand Penny sit next to him. Even Amy looked confused when he didn't.

'Should I move Sheldon?' Amy finally asked, looking at him unsurely.

The physicist looked towards Penny for a barest millisecond. A millisecond that held a thousand words.

'No Amy, it would be best if you stayed were you are'.

XoX

The path of true love never runs smooth. Please review.