AN: First numb3rs fic. Not sure where this came from, except I found I liked and needed more Don/Amita fanfic and there isn't any. It started out with the intention of being more hot and heavy and didn't quite end up that way. Apologies for any mistakes in the timeline. This roughly takes place around season 2 (ish).

It had started harmlessly enough – just a little competitive bantering, that devolved into flirting. Which led to more flirting, which led to, ultimately where it all really started, he supposed, a heated kiss, stolen one rainy afternoon at Calsci while Charlie worked through an equation for a case he was helping Don with in Larry's office, while Amita graded papers in Charlie's as Don waited.

It was hot, sexy, and riddled with taboo – the sense what they were doing was wrong-so wrong-but it didn't stop Amita from leaning in to steal another one, and Don obliged her, heart beating wildly in his chest, the knowledge Charlie could come skipping back in here, excitement at some breakthrough falling like a boulder at Don's feet were he to catch sight of them.

It was the first time he felt something in so long, something other than the overall dissatisfaction with his life, the mind-numbing fatigue and disillusionment that he'd been feeling with his job lately.

It was dangerous, this feeling, but when he glanced up into Amita's bright eyes, eyes that danced with excitement, he couldn't stop himself from smiling in return. They shared in the secret: that they were indulging in forbidden behavior - the woman his brother coveted and Don, the older brother, slyly stealing her away.

Well, not really, but stealing more than just one kiss as he leaned in one more time and then broke away, not missing the disappointment that flashed in Amita's eyes, the thrill that shot through his own heart again at her obvious interest and he told himself to tread carefully. There were more than just his own feelings at stake and could he really risk his brother's partnership, his relationship with Charlie, because he couldn't control the urge he felt to kiss his brother's…whatever it was he and Amita were to each other.

Girlfriend wasn't right -they had only been on one disastrous date, and Charlie hadn't initially seemed too optimistic about more following, but that had been weeks ago, and Don realized he didn't honestly know if there had been anymore, but felt that his dad, or Charlie, or someone would have said something had there been another one. So where exactly did that leave Amita on the available list?

He shared a tiny, relieved smile with Amita when Charlie came rushing in, oblivious to what had just occurred between Don and his former grad student. Glad he hadn't given into the temptation to pursue another kiss, maybe something more, in the time between the last one and Charlie's appearance. He focused his attention on Charlie and ignored the yammering in his heart and his mind and tried to avoid looking at Amita again. Failed, and caught her looking at him.

Wondered what it meant that she was looking at all.

It was like that a few more times, the looks, the secret smiles, the banter and flirting. Calls made to his brother's cell, dutifully picked up by his informal secretary Amita (making it apparent his brother had forgotten about his cell again, lost in a haze of numbers, or was down in Larry's office, or lecturing) became opportunities to stoke the fire between them. Once brief, to the point calls now lingered.

There were no more stolen kisses, though, on any subsequent visits, and Don made sure to not find excuses to go and see her or approach her alone. Which worked well at keeping the oblivious third party in all this, Charlie, in mind until the day when Amita apparently took it upon herself to come find him at work, sans Charlie.

"Amita, uh, hey," Don said, taken by surprise to find her at the entrance to his cubicle, looking even more beautiful than usual, clothes a little sexier - maybe like she might have made a little extra effort even? He thought her eye makeup might be a little heavier, her lips glossier. And was all that effort for him?

"Hey, uh, hope I'm not interrupting you at a bad time," she said, smile sweet and hesitant.

"No, I was just making some phone calls, trying to narrow our list of suspects," Don said, rubbing his palms over his knees and, remembering his manners, flashed a brief smile at her in welcome. "What's up?"

"I think I might be able to help with that," she said. "Narrowing your list," she added.

Don's eyebrows rose in surprise. "Really? That would be great," he said sincerely. "When I talked to Charlie, he wasn't optimistic that he'd have something that would narrow the field for me so soon." Something flashed across Amita's face, darkening her expression a little before she forced another smile.

"Yeah, he wasn't convinced that this would help, but I think it will, and I mean it can't hurt to try, right?"

"Yeah, anything has to be better at this point," Don agreed, brow furrowing slightly, wondering at the dissent between Amita and his brother. "So, what do you need?"

Twenty minutes later, they were in Don's SUV, cruising down the 405, Amita turned slightly toward him on the passenger seat, an open laptop on her lap as she explained the algorithm she had created to him. Her window was slightly cracked open and it blew long dark wisps of her hair around her face.

"So why doesn't Charlie agree," Don asked when she had finished arguing her point. She frowned again, glancing up from her computer to look at him. "I mean, it's unusual that you guys don't see eye to eye."

"Not really," she said flatly and Don chanced a look at her. He raised his brow questioningly when she met his gaze and she pursed her lips.

"We've been fighting a lot lately," she murmured and the other brow joined its sibling on Don's face. About what? he almost asked, but bit down on his tongue.

"Don't get me wrong, he's brilliant, I mean, I don't dispute that, but he's not right about everything," she said after a moment, and Don wondered if the comment was meant to refer to the math ability, or something else, maybe less quantifiable. "And trying to argue that with him," she said, trailing off and Don huffed a laugh.

"Yeah, believe me, I know," Don said dryly, "but when it comes to numbers it's hard for me to have the upper hand in that scenario. He can out-math me any day of the week. You at least give him a run for his money."

"Ha," she said, smiling shyly before sobering. "It's hard to do that when he won't even listen to what you have to say," she said and Don frowned again, wondering at his brother. "So I thought I would present it to someone who would probably listen, and if it doesn't work out, well, at least we tried, right? It's the opportunity to grab more data."

"Right."

And it did work. Mostly. It gave them more information than they had, and Don leaned over the armrest, trying to look at the screen Amita was inputing information into but it mostly looked like gibberish to him and he found his attention wandering to Amita's face, the look of concentration and happiness that at least some of her work was being validated.

His brother was an idiot, genius not withstanding.

She glanced up and caught his eye, smile softening as their eyes locked together.

"What?" She said self consciously.

Don shook his head, watching as her own eyes skimmed over his face.

"What?" She insisted.

"Nothing," he said, "you're just really hot when you're all proud of yourself. It's cute."

Jesus, did he just say that? He resisted an outward cringe and tried for a winsome smile instead and Amita laughed, shaking her head. The sound was beautiful and set Don's heart thumping again.

"Well, couldn't have done it without you," she said modestly and Don nodded in agreement.

"True," he said. "I did drive you here."

She nudged his elbow with hers and laughed again. "You did more than that."

"Yes, I also bought you a half-caf, non-fat soy latte," he agreed, face twisting in a mock shudder, and Amita laughed again, another beautiful peal of amusement and Don smiled boyishly.

"Yes, that was critical to all this working," Amita said seriously, a dimple betraying her.

"So I see."

"I never did thank you properly for that, did I?" She said, and, before he could start to answer she leaned over and quickly pressed her mouth to his cheek and that rapid thumping that was going on inside his chest ratcheted up a couple of notches. Her mouth lingered there, against his cheek, long enough that reason and good sense fled him, and he turned his head to capture her mouth with his in a solid, heated kiss.

His pulse exploded as they deepened the kiss, Amita turning towards him more fully, enough that when they finally broke away, she was leaning over the armrest, elbows supporting her, hands fisted in his shirt collar. Her laptop was caught by the dash and the armrest, wedged tightly in the space, forgotten between them as Don raised his eyes to hers to find them darker than he'd ever seen them, glittering in the afternoon sunlight. He pressed one more kiss softly against her lips, an apology of sorts, but for what exactly he wasn't sure, except the complicated mess he was slowly embroiling he, Amita, and the unwitting Charlie into, and pushed himself back against the driver side door, away from temptation

"You're welcome," he said, after a moment where he tried to slow his breath. Amita quirked a brow, obviously thinking he was full of himself before remembering the reason the whole kiss started.

"Oh. Right," she said, and shared another secretive smile with him.

"I'll have to buy you some more," he added, and wished he would just shut up, because now it sounded like he planned to do that again, and this worked much better for his conscience if this kept happening suddenly, and without warning or conscious thought on his part.

Not that Charlie would ever believe he hadn't been fully aware of what was going on when he was kissing Amita. He was doing something with a woman that Don should know – did know – was off limits.

And that Don, who Charlie often accused of keeping such a tight rein on his emotions, had let himself get carried away with her.

That he could have stopped this from ever getting to this point at any time, if he had wanted to.

The problem was, he hadn't.

While it was rare for him to show what he was feeling outwardly, it didn't mean he didn't have any at all. He felt things deeply: passion, despair, hope, love, anger, sadness, all of it. Was something of a closet romantic anyway, hoping to find that one girl he could love for the rest of his life.

Becoming more and more skeptical that would ever happen. Work had been wearing him down ever since, well, mom died, he supposed, maybe longer, but it seemed in the last year that it had been exacting a heavier toll on him. A strange melancholia seemed to be taking over as he took stock of his job and his life, and the path he seemed to be on.

Which was why his interest in Amita was so fraught with disaster.

If it was anyone else, he probably wouldn't have hesitated to take things further. Except Amita wasn't anyone else. She was the woman his brother had set his sights on: a beautiful, gifted, and incredibly intelligent young woman who could challenge his brilliant brother.

Besides, even if Don were to pursue something further with Amita, how likely was it to work out between them? Risking what would probably only end up being a fling just to make himself feel better at the expense of his brother's heart, wasn't a wise decision. At this point, he didn't think he could look one more failed relationship in the face.

His life lately seemed lonely and exhausting, married to a job that showed no mercy.

Amita was only in his life because of her association with his brother and the work they did for Don and the FBI – work that gave Don one of the best solve rates in the whole organization. He was risking a lot of things, to entertain the notion of what ifs with an admittedly extraordinary woman.

And if he didn't realize the scope of that now, there was going to be hell to pay, for everyone, later. Not to mention the irrevocable damage to an already fragile relationship with his brother.

"Maybe you should just buy me dinner sometime," Amita said playfully, breaking into his thoughts. Her dark eyes looked at him hesitantly, uncertainly. Hopefully. It was like she knew the offer would probably be rejected, Don polite, almost apologetic. The voice of reason would prevail - Don would nip this in the bud, unwilling to risk hurting his brother. That he knew whatever was going on between them wasn't just harmless flirting, but couldn't go on, anyway.

Worse, was the knowledge that whatever it was, Amita was fully game to explore it further, making resisting temptation all the more harder.

It should be rejected.

Dinner was a bad idea.

One that didn't stop him from making plans with her days later, a moment of weakness, after another half dozen calls between them, and a handful of not subtle hints on the phone from Amita. He felt something had irrevocably been set in motion by agreeing to see her again.

He told himself he would use the dinner as an opportunity to talk about all the reasons why it would never work out between them, or why they needed to end it now, before it really went too far, a sort of breakup dinner, except, well, they weren't even really going out, were they?

Their first and last meal, right?

It had been his honest intention, to let her down gently.

Except she looked amazing when he picked her up. Wearing a satin, emerald green dress that hugged her curves, and sexy, strappy high heels that showed off her beautiful long legs. The neckline of the gown revealed a gold necklace with a pendant that was hidden in the crevice between two bronze, beautiful breasts. He'd felt his breath leave him at the sight of her and Amita had seemed pleased by his reaction, smiling softly, dark eyes meeting his, a thrill going through both of them.

She was whip-smart, funny, sweet and sarcastic at the same time, and sexy – God was she sexy, he thought, and unpretentious about all of it. She was an easy-going and refreshing dinner companion, and, shockingly, topics of conversation flowed fluidly between them, not one of which landed (very long) on Charlie or why he was the reason they shouldn't even be doing this.

They talked for a long time. He talked to her about things he hadn't really touched on with anybody in years. His childhood and growing up in the shadow of genius; his mom; college and baseball; joining the FBI and those first few wild years doing fugitive recovery; Albuquerque; some of his regrets. He hadn't felt so connected with someone in a long time. It reminded him again how painfully lonely he was, how much he kept tightly reined in, terrified to let somebody get too close, and naturally if there was a person more wrong to pursue such a step with in Amita, he couldn't imagine them. She listened attentively and let him talk, and didn't push him too hard to know more or dig deeper.

He took her home hours later, when they realized the restaurant was closing up and the staff was waiting on them to leave. He followed her up the stairs to her apartment to see her to her door safely. Ducked his head slightly when she expressed her thanks at his gentlemanly gesture, and didn't offer any resistance when she asked him to come inside for a drink.

He guessed it was what they had both planned on happening, anyway.

She handed him his promised drink and took a seat beside him on her sofa. Thanked him for dinner, long, tan legs tucked underneath her. She had kicked her heels off sometime between unlocking her door and playing hostess as he drifted around her living room, taking in the family photos and books, cds, and magazines. She had eclectic taste, he noted, and studied a couple of the titles before hearing her come in behind him.

Her knees kept brushing against Don's thigh on the couch, but neither she nor Don moved to make more space between them as she propped an elbow against the top of the sofa and leaned her head against her hand and studied him.

"This was the best night I've had in a long time," she said. Don smiled distractedly in response. She really had great legs, he thought, laying a hand hesitantly just above her knee. The skin was as soft and silky as it he imagined it to be. It was the last coherent thought he had when she reached out and ran her fingers through his hair, and then leaned forward to place a soft, sweet kiss on his mouth. He was inexplicably undone by the gentleness of it. Returned it by pulling her closer, deepening the kiss, tongue exploring. His hand inched up her thigh, as hers slid along the side of his face, his stubble scratching lightly against her palm.

They parted, eyes locking, and embraced more fully, Don's hand pushing the hem of her dress up her thigh, Amita using both her hands to slide on either side of Don's jaw, pressing an open mouthed kiss to his. He moved his other hand to trace his fingers over the gold chain hanging around her neck, following it over her collar bone, the swell of her breast, down towards the crevice. They broke apart again suddenly, out of breath and Amita's eyes dark with desire.

He was in her bed less than ten minutes later, his curiosity about the mysterious pendant that hung between her breasts satisfied, her dress gone, his shirt, shoes, and pants too, soon her underwear and then his, and all that hung between them was that gold necklace and the distant memory that this probably shouldn't be happening.

They were served with a rude awakening on how bad a decision the night before was when they were interrupted by Charlie pounding on her door at 6:30 a.m.

He had just finished showering, Amita still lying naked and half-asleep in bed, hair tousled around her face and pillow. She had given him a shy smile when he had grabbed his watch off the night stand. Had lazily slung her arms around his neck when he perched on the side of the bed beside her to slide it on his wrist and took a moment to lean down to kiss her. Pouted prettily when he pulled away and declined her invitation to fix him breakfast, accepting another kiss as a rain check for later, and he was pretty sure, despite whatever his intentions before that there was now going to be a later.

The knock came ten minutes later when Don was checking his messages, and Amita had finally risen from the bed and was pulling together her clothes for the day. At first it didn't register with Don, engrossed in listening to a voice mail from Megan the night before, but Amita immediately paused in garment collecting, brow furrowing in confusion. It came again, more insistent, and that time Don heard it. He looked over at her.

"You expecting anyone this early?'

"No, I mean, the only one who would come over this early would be…"

Charlie.

They looked at each other again, the hazy, night-well-spent feeling that had been coursing through Don's veins freezing instantly when he heard it.

"Amita?"

"Shit, Charlie," Amita said, looking at the clothing she had amassed, and then hurriedly throwing some of it on.

Shit, was right.

"Why is he here this early?" Don asked, trying to delay the sense of dread he felt creeping in.

"Who knows?" Amita muttered. "Probably something to do with the theory he was working on."

Of course. Numbers. The case. He wouldn't know that Don had just spent the night with Amita. Right? Unless…maybe he came by last night and saw Don's car? Decided to confront his asshole of a brother first thing in the morning as he slunk out of Amita's apartment with a decided lack of shame?

"I'll get rid of him," Amita said. Don swallowed and nodded, wondering how they should play this out. He was too old, technically, to hide in a closet or go climbing out a window and down a fire escape, but that didn't stop him from considering both for a second.

They were all consenting adults here. By all counts, and Amita had said as much last night, it had only been that one disastrous date between Amita and Charlie that had occurred weeks ago. She was technically free to date whomever she wanted, except Charlie would think that Don should know better than to consider her on the market. It was the unspoken rule, after all, especially after that whole debacle with prom all those years ago.

Don should know better.

Problem was, Don didn't care last night. It was easy enough being with Amita to forget Charlie existed.

Amita closed her bedroom door behind her and Don sat on the bed, ears tuned to the sounds beyond wondering what he would say to Charlie if confronted.

"Hey, Sorry, did I wake you? I thought you'd be up already," he heard Charlie say.

"Yeah, sorry…I overslept," she said, and she sounded a little breathless. "What's up?"

He heard rustling sounds; the sound of a chair scraping across the floor.

"I think I may have it figured out," he heard Charlie say.

"Oh, um, what?"

"Don's case. His suspect pool. How we can narrow it down."

"Oh," he heard Amita say distractedly. "Oh, right. Uh, he didn't tell you?"

There was a pause, and Don could just imagine Charlie, in the process of setting up whatever equation he was about to explain, looking up at her curiously. No, Don had not told him. Why would Don have admitted to any time spent alone with Amita? Not that, prior to today, that it would have been any big deal, but he could see now how it might be laying a pattern of behavior for Charlie later if he came to realize something going on.

"No, actually, I haven't seen or talked to him since Tuesday morning."

"Oh. Oh, well, I developed an algorithm using the methods I told you about to narrow it. It worked." This was said a little more pointedly, and Don figured Amita was still a bit sore at having her work dismissed outright by his brother.

"Oh, um, okay. It did?' Charlie sounded skeptical.

"Mostly," Amita replied, a bit grudgingly. "We were able to triangulate the area that we think has the greater probability for suspects, and eliminate about 85% of the candidates."

"Oh, oh, well, that's good. It's a good start. Larry and I think we have a formula that can narrow the field even further. With a 95% or better probability. Here, I'll explain." Don perked up despite himself, rudely reminded in Charlie's arrival that he still had a case to solve and could use whatever help he could get to get it done.

"Great," Amita said, not sounding impressed or enthused. Then again, she was supposed to be trying to herd Charlie out the door, and from the sound of it, it seemed more that Charlie was settling in.

"Well, you can explain it all to me later," Amita said, confirming Don's line of thought. "I still need to shower and get dressed. I look a mess."

She looked freshly fucked, and beautifully so, and Don hoped that Charlie didn't recognize the look, since he was liable to ask questions.

"No, you, you look…great," Charlie stuttered, and Don winced, hearing the sincerity in his tone despite the delivery. "And I-I can wait. I was hoping I could ride in with you. I took the bus. We can discuss the theory on the way to the FBI."

"Oh, you don't have to wait on me. I might be awhile," Amita said hurriedly.

"Oh. Okay, well, I guess I could call Don for a ride," Charlie said, after a second. "I tried to call him last night but all I got was his voicemail." Don's eyes widened and he frantically grabbed for his phone to mute it before it trilled in the apartment and gave away his position. He had turned it off last night, sometime during his and Amita's dinner, deciding he didn't want distractions or an excuse to leave her. He was still going through his messages this morning when Charlie had shown up at Amita's doorstep just after dawn.

"I think he said something about an early morning meeting or something," Amita said uncertainly, voice trailing. "When I talked to him, um, yesterday. You don't want to call and interrupt. It sounded important."

"Oh," Charlie said. "I guess I can call dad."

Don sighed and looked up at the ceiling.

That would be perfect. Both Amita and Charlie and his dad over here. If Charlie hadn't noticed his car in the parking lot then Dad surely would. Since the bus let off at the front of Amita's apartment complex and the tenants parked in the back, it might explain how Charlie had missed it.

He felt for sure Dad wouldn't, but maybe because it was his dad that always seemed to have a sixth sense for when Don was up to questionable behavior.

"Oh, you know what, never mind. It's fine. Just, uh, um…Let me just…do something…with my hair and I can take you in just a few minutes."

"I don't want to rush – I mean, I can wait, I don't mind. You said you were just getting ready to take a shower?"

"Yeah, I mean, it's 6:30, Charlie," Amita said with a self-conscious laugh. "It's a little early. I still haven't had coffee yet."

"Right," Charlie said. "Sorry, I didn't think about the time. I just – I figured it out and –Seriously, I can wait. I'll just fix us a couple of cups and read the paper or something while you get ready. Take your time."

"Oh, um, thanks, but you don't have to do that. I'm sure you didn't realize…about the time," Amita said. "And, well, this is important, right? Let me…just…give me a few minutes."

The window option was sounding more and more likely, Don reflected, glancing out of it, especially since now he was going to have to beat feet to the FBI before Amita and Charlie got there. He stood and examined the window closer. They were three stories up. It wasn't the first complex he'd climbed through a window and down a fire escape from, although all the times before (with the exception of one, he reflected ruefully), he'd at least been chasing a suspect.

He heard soft footfalls and a second later Amita reappeared, closing her bedroom door behind her, a hand leaning on it.

"What are – are you seriously thinking about going out the window?" She whispered, mouth twisting in surprise.

"You got a better suggestion. It's not like I can just waltz out the front door."

Although he could just imagine the expression on Charlie's face if he did.

"I know. I'm sorry, he won't leave!" She whispered. "Look, you don't have to climb out the window. I'll finish getting dressed and take him to your work."

"You're going to have to take him to breakfast or something, because I still need to beat you there and it's getting to be rush hour traffic."

Amita swore and rolled her eyes. "Maybe I could take him to Calsci?" She suggested.

"That would be even better," Don said, and Amita nodded, biting her lip.

"This wasn't a mistake," she said, and Don looked up at her. "I don't regret anything that happened last night."

"Doesn't look like the best decision I could have made, though, spending the night," Don answered quietly.

"I'm not sorry," Amita said, moving closer and Don looked away.

He wasn't sure he was, either, but Charlie had no idea that Don had moved in on with what he considered his girl, without any idea that something had been going on between said girl and his older brother for a while now, right under his nose.

The realization would be devastating to say the least, and Don owed him an explanation before he found out in the most painful of ways.

"It's complicated, between Charlie and me," Don said and Amita nodded reluctantly. "We were never very close growing up, for a lot of reasons, and what you and I did…that's not going to help that. I shouldn't have let this happen," Don said quietly.

"You didn't let anything happen. It's what we both wanted. There's something there, I know you feel it, too, Don. I don't want Charlie getting in the way of us, and I don't want me getting in the way of you and him, and I don't want to have to stop seeing you," she said, voice wavering, eyes locked on his and he could see the depth of feeling there.

"Amita," Don breathed, and she cut him off with a kiss.

"Just give me ten minutes," she whispered "and we'll be gone and then you can leave." He nodded, watching her grab a hair tie and loop it through her hair in a pony tail. She kissed him again after she grabbed her shoes and socks, a long, deep kiss, and he returned it feverishly, grabbing her face between his hands before remembering they didn't have time for passionate, leisurely kisses, but it felt like it might be the last time he got to kiss her.