Disclaimer: Maybe I shouldn't say anything about the matter, but I'm gonna say it anyway: Numb3rs and its characters don't belong to me, but to CBS. This is a work of fiction. Any resemblance with actual names, characters, places and incidents are either products of the author's imagination or used fictitiously.
Rating: T
Timeline: season 4
References: to 1-03 Vector and, less explicitly, some others up to and including season 4.
A/N: This had been planned as a story for the ABCs ('N' like 'NSA', which was a title idea from both whatever55 (thanks for all your input!) and myself), but turned out to be too long for that. It's plotted out and mostly written, so I'll try to post weekly.

Chapter 1: A Homicide

"Hey buddy," Don greeted his brother and stepped out into the bright afternoon sun to hold up the crime scene tape for him, "thanks for coming."

"No problem," Charlie replied as he ducked under the tape. "So what's the story?"

"The victim's name is Andrew Bourgeois, 46 years old, divorced with a teenage boy who lives with the mother, worked in IT at a big telecommunications company. He lived here and we assume that he knew his killer and let him in himself sometime last night; a neighbor found him this morning. From what it looks like, there was a struggle, and in the course of that, he suffered a blow to the head. The coroner says he was probably dead within minutes, that is probably around midnight, but we'll have to wait for his report to be sure about the time and cause of death."

"Okay," Charlie nodded as he absorbed the information. By now they had reached Bourgeois's home office and he swallowed when his eyes fell on the body bag in the corner. He quickly tore his eyes away and forced himself to focus on the technicalities of this case. "So what exactly am I here for? You said something about a notebook?"

"Yeah, I did. Gerry?"

A member of the CSI unit turned around with a look on his face that seemed almost grim, as if it was a cardinal sin to interrupt him in his work.

Don, however, seemed completely unperturbed by that. "Mind showing him the notebook?"

Gerry inspected Charlie from head to toe and Charlie had to fight hard to stand the scrutinizing stare without flinching. "No touching. Are we clear on that? We only dusted the outside so far."

"Understood," Charlie said and had to clear his throat to win his self-confidence back. He wasn't sure how the guy did it, but he had an air of natural authority about him that was quite impressive. When the stern look still wouldn't vanish, Charlie put his hands in his trouser pockets. Better not be tempted.

"We found it in the inner pocket of his jacket at the wardrobe by the door, together with the receipt," Don explained. "The receipt tells us he bought that thing a little more than a week ago, but it's already more than half full, so we assume that whatever it is that's in there was important enough for him to take it with him wherever he went and work on it. We compared the handwriting to the other documents lying around, it seems to be his."

"So what exactly did he write in there?"

"It seems to be some kind of computer code. Look," he said and held the small book open with the gloves he was wearing, careful not to smear any fingerprints that might be on there. Gerry seemed to be appeased by Don's diligence and resumed his work.

Now that his fierce eyes were no longer unsettling him, Charlie could concentrate on the code he was seeing. The first page merely showed some very generic lines, the definition of the variables being used and the sort. That was what the victim had written down at the bottom of the page as well. Apparently he'd first written the code in pieces and had then, in a different color, added his thoughts or comments about it. What Charlie wasn't clear on, however, was whether this was a code that the commentator was developing himself or whether he had copied it from somewhere and was now trying to decipher it. With both options, Charlie found it strange that Bourgeois would have used a notebook to write down his ideas by hand instead of simply typing them into a suitable program immediately. On the other hand, Charlie was too often teased for writing on chalkboards as if he had dared to judge this way of working.

"This far, this is all very basic and generic," he explained to his brother, "I can't tell you anything about the program going merely by that. Can you turn a page or two?"

Don did and held the notebook out towards him. Charlie skimmed the pages, but soon slowed down.

"Turn another page," he said as he was staring at the symbols in the small book. On the next two pages, there was only code, no commenting, and thus a lot of data for Charlie to absorb and check his theory. He pressed his lips together and tried finding his mistake, but he couldn't, everything fit. He shook his head. This was wrong. This just wasn't possible...

He was clenching his hands to fists, which he was still hiding in the pockets of his jeans. The tremors that went through the rest of his body, however, couldn't be masked that easily. His biggest problem was his voice. The way he was feeling now, everyone around him would notice that something was up as soon as he would open his mouth, and he couldn't let that happen, he had to hide his agitation.

Alright. Calm down. Breathe.

And he did breathe, although he was careful to draw in the air through his nose, slowly, not letting it show on the outside how much difficulty he was having on controlling his basic bodily functions.

"Charlie, I'm talking to you."

Charlie flinched, turned his head and was confronted with that familiar expression of annoyance on his brother's face.

"Sorry," he said and cleared his throat, "I've been thinking."

In the back of his mind, he realized that the look of annoyance was still on his brother's face, still hadn't been exchanged for mistrust, and for once he thanked his nervous disposition – and his disposition to get easily lost in his head whenever he was highly focused on something. His flinching and his tendency to block out the rest of the world had actually helped to make it more believable that he was really just absentminded instead of highly disturbed by what he was seeing.

He couldn't think about that now though, but had to put up his best show to appease Don, who was standing there expectantly. "Care to share?"

Charlie regarded the notebook while his mind was racing in order to find a way to keep up the facade. For as long as he didn't know what was going on here, he couldn't let anyone know of the significance of that code, so he had to do the best performance of nonchalance he was able to. He was well aware that Don could read him like a book, so he had to make sure that today, that book remained firmly closed.

"It's a bit difficult to explain," he said in order to buy time, but even while he was saying the words, an analogy was forming in his mind, and now the pieces were automatically assembling, making the rest easy for him. "You know, writing a complex code like this really is just about putting very basic pieces together in a unique way, like building a castle with building bricks. You can put them together in any possible combination, sometimes that'll result in something that resembles a building, that is a code that works, and sometimes all you get is an unstructured heap of bricks, that is a code that doesn't work. Now, in order to figure out what this code is for, that is what kind of building we're looking at, I need to analyze the way in which the components are connected to each other, the code's structure, and the first step to do that would be to analyze which items, that is which brick types, have been used more often and which ones less often, and in which context. If I'm going to do that, it would help me a lot to have that code completely, and digitally, so you should look where he saved it on his computer and make me a copy of that file." He indicated the computer screen they were facing and that was still up and running.

"Yeah, there might be a problem with that," Don said. "According to the CSI guys, the computer was running when we got here, but it seems as though the harddrive has been wiped clean. Our people are going to try and restore the data of course, but for now, this notebook is all we have. So any ideas what this code could be about? Any unusual patterns you see?"

Charlie bit his lip. He'd thought to have wriggled out of this dilemma rather neatly, so he wasn't at all thrilled to talk about this code any further. To tell the truth, he was still trying to hide the tremble of his hands. For a moment, he considered telling Don everything he knew, that he knew very well what this code was supposed to do, that in fact, no one knew that code better than himself since he'd been the one to write it. He knew he couldn't do that, though, certainly not here where a dozen of other agents could listen in.

He took another deep breath, disguising it as a sigh. He didn't like this one bit, but the fact was, he couldn't tell his brother anything as long as he hadn't figured out what was going on here. He needed to know how on earth that dead man had gotten hold of a code he most certainly wasn't supposed to have. All the while, he had to try not to think too much about the fact that not only had his code turned up here, but also that the guy it had turned up with had turned up dead.

He shuddered, despite himself, and forced himself to focus his attention back on Don. "I don't know," he said. "Can you tell me anything else about him? What did he –"

He stopped short, suddenly remembering what Don had told him about the murder victim earlier. "You said he was working at a telecommunications company?"

"Yeah, why? Does that help?"

Charlie shook his head and ran his hand through his hair, then stopped when he realized that he shouldn't show his nervousness to Don. "I don't know, it could." He could see Don was frowning, he was starting to suspect something, so it was high time for him to get out of here. "Look, I'll see what I can do, alright? I have to go now though, I forgot I had a meeting in a couple of minutes."

"Alright," Don said, but the frown was still on his face. "I'll make sure you'll get a transcript of that then?"

"Yeah, of course, thanks. I'm sorry, I really need to go now," he said and hastened to get out of the house.

"Alright," Don repeated as he accompanied him to the front door. "Thanks for stopping by."

Charlie just waved at him without stopping or turning around and hurried to his car.

Since he was afraid Don might watch him from the house, he drove away and only stopped after a block or two so he could think. He needed to figure out what to do, and fast. For a moment, he wondered if he shouldn't just have told Don what he knew after all. It felt wrong keeping crucial information from him in a federal case, and it occurred to Charlie that he might even be committing a criminal offense by withholding that information. On the other hand, he would most certainly commit a criminal offense by telling him, so he didn't really have much of a choice here.

So he couldn't tell Don for the time being, thus he had to figure out on his own what to do next, and to do that, he had to figure out how on earth the dead guy had gotten hold of the code. Or was he supposed to have it? Maybe he was an agent or consultant with the NSA as well? Maybe his job at the telecommunications company was only a cover? Maybe his task had been to check the code that Charlie had developed for them? That wouldn't be too far-fetched, even though they should have done that before now, before a week ago when the guy had bought the notebook. And if he had been hired by the NSA to analyze Charlie's code – then why do that at his own home, without any further security measures, at least concerning the notebook?

No, looking at the big picture, there was little chance that the dead guy had gotten hold of the code in a legal manner, and if that was true, then it meant that there was a security breach within the NSA, and that alone was enough to send shivers down Charlie's spine. He was positive about his deductions, though: if that code had showed up here, there was a high probability that someone working for the NSA had leaked it, and considering the code's purpose, Charlie had difficulty thinking of a reason that didn't entail criminal intent.

So he'd have to inform his bosses at the NSA about the leak, that was the easy part. The more disturbing question however was: if the guy that had examined the code had ended up dead – what did that mean for Charlie?