Disclaimer: see chapter 1

Chapter 6: Making Progress

Charlie felt a little lost, and truth be told, he was. Granted, he had managed to find his way up here to the floor that housed Don's office, but he had no idea exactly where to find the person he was looking for.

"Mr. Eppes!" a voice called out, and when he traced the sound-waves back to their source, his eyes fell on the bald agent that, together with the sandy-haired one, had conducted his initial interrogation two days ago, Agent Sinclair, if he wasn't mistaken.

"I'm sorry, Doctor Eppes," the agent corrected himself before Charlie had the quickness of mind to say something in return. "Or should it be 'Professor'?"

For a moment, Charlie pondered whether Agent Sinclair was mocking him, but he couldn't find any indication of that. "I really don't care," he said eventually, after he'd decided that doing what he normally did and throwing out all the titles and the 'Eppes' in exchange for a much simpler 'Charlie' wouldn't have felt right in this situation, not when he was talking to someone who, up until few hours ago, had considered him a severe threat to national security.

"Don's not here," the sandy-haired agent inserted himself into the conversation, Agent Granger. "It'll be a while before he returns."

Charlie nodded. "I know." In fact, Harvey's assurance of Don's absence had been what had made Charlie come here so readily. Even though he could somehow understand the FBI's actions and respect his brother for the job he was doing, he wasn't particularly eager to run into him anytime soon.

"Wait a second," it then occurred to Granger before Charlie had time to bring forward his request, "how did you get up here? You need someone working here to walk you around."

Charlie frowned. "Agent Miller assured me that I didn't."

"If he's been working for the NSA, he'll have clearance," Sinclair reminded his colleague.

"Yeah, but not a high enough clearance to just waltz in here," Granger insisted, but a certain doubt had crept into his voice. He turned his head to study Charlie more thoroughly before he seemed to come to the conclusion that asking him directly was the more productive approach, "Do you?"

Charlie tilted his head and shrugged, thinking hard about what to say. "It's either that or I managed to overpower your security guards downstairs," he finally settled for an evasive answer that should tell the agents enough, but nothing more. Harvey and the other NSA agents he'd been working with over the years had always strengthened the importance of not telling people more than necessary about his work, including his security clearance. One could never be too careful.

"I'm actually looking for Agent Miller," Charlie finally put forward what he'd come here for, desperate to get out of this conversation.

The two agents exchanged a glance before Sinclair took him to a small room at the far end of the bullpen.

"Thanks," Charlie said quickly and squeezed through the door before Sinclair even had time to finish the surprisingly gentle 'No problem'.

"Charlie, hey, I'm so glad you changed your mind," Harvey greeted him with a forceful pat on his shoulder.

Charlie cast down his eyes and cleared his throat. "Yeah, about that, I'm… I'm sorry for how I acted this morning. I was… a bit overwhelmed by your suggestion, I needed some time to clear my head."

"Well, the important thing is that you're here now," Harvey graciously accepted his apology and immediately turned to business, and Charlie was grateful for it. Finally, there was something he could work with, something that was clear and easy to understand. It was only a second later that he became aware of the irony, of how far less difficulty he had deciphering a code than figuring out how to deal with Don and his fellow agents – and with the possible terrorists he'd recently met.

Don felt exhausted when he and Megan returned to the office. It was late in the day, and their most recent house search hadn't yielded any results, at least not of yet, but Don doubted that forensics would find anything that they hadn't found so far. Ever since both Charlie and Rodney Cross, the guy that Don had arrested during the raid, had been cleared as suspects, they had been focusing on Jim Fennigan, someone else who, as Charlie had told them, seemed to be one of the leaders of the group. But leader or not, there wasn't anything to connect him to terrorist activities, at least not if one didn't count the attack on the oil company.

"Did you ask your brother to come back?" he was greeted by Colby.

Don raised his eyebrows in surprise. "What? No."

The unspoken question had to be clearly visible on his face, for Colby explained with a nod towards the room they had given Miller as a temporary office, "He's been in there with the NSA guy for hours. I guess he's helping him decode the messages."

Don turned his head to look at the closed door, a frown appearing on his forehead. "He is?"

"So you, too, have no idea what changed his mind," Colby clarified.

"I stopped years ago to try and understand what's going on in his mind," was Don's mumbled reply as he was busying himself with sifting through the folders that had been put on his desk in his absence. At the same time, he was keenly aware that his statement was not correct. Yes, he'd stopped trying to understand Charlie's math explanations even before his little brother had started attending elementary school, but he'd never had any trouble understanding his brother's reasons for doing or not doing something – never before this case.

"That's interesting," Colby said, and in such a strange tone that it made Don look up at him.

"What do you mean?"

Colby took a look around, thereby including David and Megan into the conversation, who'd been listening to their exchange. "Come on, I can't be the only one who thinks this is pretty weird. You know I don't mean any disrespect, Don, but you gotta admit, it doesn't seem very clever to give someone, who so far has been a suspect, access to everything that we've learned in this investigation."

Don was shaking his head, a feeling of irritation awakening within him. "What do you want me to do? It wasn't my decision."

"But you weren't particularly fighting it either."

"Because I thought Charlie had turned his back on this anyway!" Don gave back a little heated. "Besides, whether or not it was my decision, I don't think that any harm can come from him working on this case. I'm not sure what good it's supposed to do either, but if the NSA wants him on this, let them have it."

Before Colby could object anything to that, the door to Miller's office was opened and he came striding towards them, closely followed by a bent-down curly head that Don was only too familiar with.

As it was, the curly head froze on the spot when he set eyes on him. "Don! You're here."

Don raised his eye-brows. "I am. In contrast to you, I actually work here."

He wasn't sure what it was that had made him say those slightly offhand words, he only knew that there was something that he didn't like about the idea of Charlie having snuck back to work with that NSA guy. Anyway, the words were out now and couldn't be taken back again.

"We've deciphered the messages," Miller said while Charlie was still staring at him with that look on his face that had always reminded Don of a wounded puppy. "Or more to the point, Charlie has. Where should we go so he can present you his results?"

As an answer, Don led the group into a conference room, where Charlie connected his laptop to the projector, showing them the rows of numbers they'd become familiar with and that, so far, they hadn't had any idea what to make of. The fact that Charlie, within a couple of hours, should have been able to decipher them seemed too good to be true, so Don figured that Miller's announcement had been more bragging than truthful. But at the very least, Charlie seemed to have found a lead on how to decode those messages, and if that would keep him and the NSA guy busy for the next couple of days, all the better.

"Alright…" Charlie started and had to clear his throat. Even so, his nervousness seemed almost palpable, at least in the beginning. Once he had talked himself into the subject though, once he'd dived into his math world, the nervousness was gone. "So as you can see here, the coded messages consist of rows of numbers without any spaces to separate them from each other. What became obvious pretty soon though is that in each message, the number of digits is divisible by four." He pointed at the four examples he'd pulled up on the screen. "You see, here we have 84 digits, here 116, here 92, and here 56. It's the same with all the other messages, so that suggests that each unit of meaning is represented by a group of four digits."

"Unit of meaning?" David interrupted his soliloquy.

"A linguistic entity, something that makes up our language. A word, for example, is a unit of meaning, or a syllable. In this case, each group of four digits stands for a letter in the alphabet."

"And that helps us how?" Colby asked without making much of an effort to hide his skepticism.

Charlie, however, either didn't notice the undertone or didn't care. "Now that we know what a unit consists of," he explained, "we can take a look at the frequency distribution. Usually, you can draw conclusions from that, at least if you know what language the message is written in. I assumed the texts were written in English, and in the English language, the most frequent letter is e, followed by t, a, r and so on, so in a first examination, we would expect the most frequent group of digits to represent an e, the second most frequent group of digits to represent a t and so on, through all 26 letters of the alphabet. When we list the different groups of four, though, we find that it's far more than 26 different sets."

"So the digits do not represent letters," Colby concluded. Don had the impression that he was getting a little impatient, and somehow, he could understand that. He knew his brother though, he knew that look on his face. Charlie had found something, something that he considered important, so now, he wanted to share his knowledge, and for that, he knew he needed to start with the basics.

"That was one possibility," Charlie admitted. "Another possibility was that each letter has several different ways of being encoded, which would make it harder for outsiders to decipher the messages. But, since the group wanted to make their messages more easily legible for themselves, each letter has one encryption that ends with a two, and that's when it's the last letter of a word."

"Hold on," David interrupted him, "how do you know that? Wouldn't you have to figure out which digits stand for which letters first before you know where a word ends?"

Charlie shook his head. "Not necessarily. You can see here that the frequency of twos is above average, especially when you only consider the forth digit in each group. The giveaway though was the endings of their messages, they always end with a two, which made it a theory worth pursuing. So what I did then is that I wrote a program that automatically inserts the same letter for same groups of four digits and goes through the different possibilities one by one, starting of course with the more likely ones."

"And how did you know which possibilities were more likely than others?" Megan asked with a look of concentration on her face.

"Well, since I knew where the words ended, I could narrow it down a little, since some letters are much more common at the end of a word than others. Besides, I had a few likely candidates for h, i, e and y, since many of the messages started with a two- or with a three-letter word, most likely with 'hi' or 'hey'."

"So did you figure out the code?" Colby asked, and Don had the impression that he'd just barely been able to hold back an impatient 'or what'.

"I did," Charlie nodded, "even though it was still a bit of a challenge, since some of the members occasionally made mistakes, which threw my program off. But once I had realized which group members were fluent in their code language, it found the right equivalents very quickly. Here they are."

He showed them a list of numbers and letters being matched with one another, and before Don could tell him that they didn't really have a use for that list right now, but were more interested in the messages themselves, Charlie clicked towards the next slide. "And these are the messages," he said while Don and his colleagues bent forward, reading in concentration.

"I'm still not sure it's going to help you any, though," Charlie continued talking. "At first glance, I couldn't find any secretive messages among those, it just seems to be a sort of exercise, almost some sort of game. I figure they may have wanted to learn this code just in case, they seem to be a little suspicious of governmental surveillance. In fact, some of the talk in these messages is about learning the code. Other messages are just about meetings or small talk, so nothing of any significance."

Don, getting exasperated by his failing attempts of reading the messages, attempts that were again and again sabotaged by Charlie's talking, decided to stop his lecture. "Why don't you let us be the judge of that?" he asked with some sting in his voice.

He immediately felt sorry for his less than friendly tone, especially after Charlie had provided them with such an important lead in this case, but before the sentiment had truly spread, Charlie continued arguing, and his antagonistic and pretentious behavior wasn't suited to make Don feel sorry about anything.

"This isn't the behavior of a terrorist network," Charlie insisted. "These messages, judging from the ones I've read, are small talk at best, there's nothing whatsoever in there about any plans for a terrorist attack. They're just using code because they're a little paranoid, they're afraid they might get shut up by the government, but if they were indeed a terrorist organization, they would be far more careful. This code, it's hardly more than a little game. If they actually were a terrorist organization, their code would be far more sophisticated than this, it wouldn't be something you can just crack in one afternoon."

"Well, from where we stand, this code is sophisticated enough," Don replied. "You can't expect everyone to be a math genius."

"But I'm telling you –"

"Thanks for your help," Don cut him off before he deliberately turned away from him and towards his team. He really didn't feel like starting a fight with his brother, not after he'd been of such help to them, and certainly not in front of his co-workers. "Alright guys, let's get a quick overview of these messages, and I think then we can call it a day. You're joining us, Miller?"

"Sure thing," the NSA agent said and gave up his standing position to sit down at the big table with them.

Out of the corners of his eyes, Don kept watching Charlie pack up his things, and despite himself, he was assailed by a guilty conscience. He really just couldn't get it right, could he? On the other hand, he told himself that Charlie was equally to blame, he just kept assuming that he knew everything better, and Don was keenly aware that the feeling that at least with regard to him, Charlie usually did, kept triggering his anger. Maybe they were simply incompatible, for one thing seemed to have become rather clear over the course of the last couple of days: whatever happened, he and Charlie always ended up fighting.

And yet, more than ever, Don found himself wishing that it wasn't so. Over the last couple of days, he'd seen a whole new side of his brother. And the way he'd worked out this code… Today clearly hadn't been the first time he'd done this, and from what they'd learned about his NSA affiliations and judging from the way Charlie had compared the group to a terrorist network, there was some chance that he'd been using his mathematical gift to fight crime for some time now. That was something though that Don had difficulties wrapping his head around, for in his mind, his little brother was quite comfortable in his ivory tower of academia, of mathematical concepts that seemed to only serve to pass the time, things that people could busy themselves with who had nothing else to worry about. Today's events, however, had shown Don clearer than ever that his brother's math was more than just a diversion for people who were overly intellectual, that it could indeed be used for real-life problems.

"Bye, Charlie," Miller's voice then interrupted his thoughts, "see you tomorrow."

Charlie gave a mumbled greeting back and a second later was out of the door. Don gave a deep sigh, as though a big weight had been lifted from his shoulders. And it was true, he had been extraordinarily tense the entire time that Charlie had been here, for he'd been feeling permanently strung up, as though he was just seconds away from exploding, from starting another fight.

At the same time, he was aware that the fighting had already taken place, and that his brother's parting wasn't something that would prevent worse things from happening, it was something to solidify the trenches, at least if Don didn't set the record straight.

"I'll be right back," he told his team members and stood abruptly. He could sense their surprised glances in his back, but he had no time to think of that now.

"Charlie, wait!" he held his brother back, just as the doors of the elevator were opening.

Charlie turned around, and it took only the fracture of a second for the surprise in his eyes to turn into mistrust.

"What, you decided to detain me after all?" he asked with a hint of cynicism that suited him rather badly.

Don closed his eyes and took a deep breath, telling himself to keep his irritation inside. "You know you're free to go. I was just wondering… are you going home?"

Charlie raised his eye-brows, the look of suspicion still on his face. "So you are trying to keep tabs on me."

"Will you stop it?" Don asked with some exasperation. This was hard for him as it was, he wasn't used to being on the begging side of a conversation, and Charlie's offish manner wasn't rendering things easier. "I was just thinking… I mean, maybe I could stop by the house after work."

Charlie frowned. "You know you can come and see Dad whenever you like without me getting in your way. Just because I bought the house doesn't mean anything's changed. Dad's my housemate, not my prisoner."

Don took another breath, slowly counting in his head to three before he went on. "That's not what I meant. I wasn't planning to see Dad, I was planning to come and see you."

The frown on his brother's forehead deepened. "You're seeing me now," he observed. "Isn't that enough?"

Don was silent. Usually, the answer would have been 'yes', and it would have come without a moment's hesitation. Now, however, he felt that it wasn't enough. "I just think it might be good for us if we sat down and… I don't know, just talked about stuff."

"What stuff?" Charlie asked in a less than inviting manner that didn't really help Don to leave his comfort zone.

"What do I know?" he exclaimed a little more forcefully than he'd planned. "But do you honestly want to tell me you're happy with the way things are between us? I mean, we're still brothers, but within 24 hours, I find myself going from considering you a terrorist suspect to learning that you've been working for the NSA! It just doesn't feel like I know you anymore."

Charlie was looking back at him, and for a moment, Don thought that his facade of cool reservedness was about to crumble, but in the end, it held. "That has never bothered you before."

Don swallowed. Maybe that was the impression that Charlie had gotten from him, but it wasn't very accurate. First of all, until very recently, Don had always felt to know his little brother quite well, maybe a little too well. And secondly, even though he'd never openly pursued a tighter relationship with him, he would have been lying if he'd said he'd been happy with the way things were between them. He just hadn't found it in his power to change things, much less after their mother's death.

Now, however, it seemed as though he'd been waiting too long to repair the bond between them. Charlie was making it quite clear that he no longer sought a relationship to him, and if that was so, there was nothing that Don could do to change that.

"You know what, forget it," he drew back. "Say hi for me to Dad."

A soft pling told them that the elevator had returned, and again, the doors opened. "I will," Charlie said quietly and stepped into the cab. Don was about to turn away, but Charlie remained standing in the light barrier, keeping the doors open. "You know you're always welcome at the house," he said earnestly. "It's your home, too."

Don only managed to nod before Charlie stepped back and the cab swallowed him up.

He took a deep breath. True, that hadn't been the reconciliation he'd hoped for, but it hadn't been the final rupture he'd feared it might become either. And maybe, despite their differences and their history, there was still hope for them after all.