Don liked spending time in his family home. No matter how long he had lived away from the house, it still felt like home, with its unique and familiar smells and sights. He was sitting in the living room with his father watching a ball game, but his brother was absent.

Don and Charlie had never been close growing up. The five year age difference as well as Charlie's extraordinary abilities had put a wedge between them that Don felt was only recently beginning to be broken down. He knew he wasn't completely past his issues with his brother and he also knew Charlie wasn't past some of his problems with him, either. Those issues were part of the reason he had tried to spend time at home with his family ever since his return to LA. He knew that even if his brother and he could never mend their relationship, at least they were giving their father the opportunity to spend time with both his boys. He never had much of that when they were growing up.

But Charlie was annoyingly absent.

"What's Charlie up to these days, dad?" Don asked, trying to sound casual and knowing his father saw right through it.

"He said something about Kalman's filter," Alan said.

Don's gaze left the TV and rested on his father, trying to figure out what the older man had just said.

Alan, sensing his son's confusion could only smile. "I have no idea what that means, but that's what he said."

Don glanced at his watch, noting the late hour. A math professor shouldn't be working at this time of the night; but his brother never had played by the rules everyone else seemed to live by. "He's working odd hours again?"

"Yeah. He mentioned something about being on a tight schedule," Alan replied, returning his focus to the game. He didn't mind his son's working habits as much as he sometimes pretended. Charlie enjoyed his work so much that he could sometimes get lost in it and Alan loved that passion. He just knew that sometimes Charlie needed to be brought back to reality or he'd starve to death.

He chuckled softly when he noticed Don checking his watch for the third time. Don never seemed to realize that the same tendencies that made him worry about Charlie, also made Charlie worry about him. They both got lost in their work and both Charlie and Alan were painfully aware that Don's job was a little more dangerous than being a professor of applied mathematics.

Don resigned to watching the ball game without his brother. It wouldn't be the first time Charlie had worked in the garage well into the morning.

1

Charlie looked at his garage wall, imagining what was happening in the house, beyond the barrier. He could hear the ball game on TV and knew his brother was probably wondering where he was. He only hoped Don would be able to understand that sometimes his work was important enough for him to be locked away in the garage, away from everyone.

He set an alarm clock to let him know when it was time to eat. He knew he would only hit the snooze button and he hoped that he would eventually get tired of playing with the alarm and go eat. He figured it worked every morning when his goal was getting up, so it should work where supper was concerned.

By the time the alarm went off for the fifth time, he knew he had to get up and go into the kitchen. He didn't really want his father or brother to come by and force him to eat. He especially didn't want them to know that he was locking his door while working in the garage. It was sensitive data he was working with and he couldn't afford to have someone walking in, even if they wouldn't understand a thing they saw. He knew that a locked door would lead to questions and his answers – or lack thereof – would lead to worry, by both his father and his brother.

His father worried too much as it was.

Charlie knew why his father worried. There was a time in the not so distant past when Alan feared he had lost both his sons. Don was in the Fugitive Recovery Squad, barely calling home and Charlie, far more detached from his father and brother, had allowed himself to sink into his world of numbers and equations. Their mother's illness had brought Don back to LA, and her death seemed to have reawakened Charlie to the world. But now he knew Alan was worried about losing them all over again, what with Don's continuously dangerous cases and Charlie's consulting work with his older brother.

Charlie walked out of the garage slowly; making sure that the door was locked behind him. Neither Don nor Alan reacted when he entered the house but he could sense their unvoiced comments. He knew they thought he worked too much, but what they couldn't seem to understand, without it being said, was that he wasn't working on just any school project. He was working on something important. There were times in his life he thought they would never understand him, that the distance between him and his brother would never be bridged. And there were times, however rare, when he looked at his brother and thought he actually got it; got him. But Don never seemed to understand what made him tick. He never seemed to understand why Charlie acted the way he did. And no matter how much Charlie tried, he could never seem to make him understand.

1 - 2

Lorelei Roberts shut her eyes tight, trying to stop the burning sensation. She knew her body was telling her she had been staring at the computer screen for way too long and that it was time to sleep, but Lorelei refused to give in to it. She had to get the results of the last run of the program to Charlie ASAP so he could give her something by morning. It hadn't taken long before she and Charlie had fallen into a familiar working rhythm with each other. She just wished he didn't have to be the gentleman all the time and insist on taking the graveyard shift. She had seen him a few days ago and it looked like he wasn't getting much sleep, night or day, and it now seemed to be catching up with him. She only wished it would all end soon. National Security was National Security, and Lorelei knew that she, Charlie and the others would do whatever it took to help the Air Force with this one, but the human body could only take so much, and Charlie was known for pushing the envelope.

The program finally finished running, and Lorelei opened the output file. She smiled as she saw the numbers her program had generated, and she printed the file. Putting it in a package, she called to the Staff Sergeant, who was standing quietly outside the office, waiting for the data he needed to deliver to Professor Eppes.

1 - 2 - 3

Don was startled awake by a knock on the front door. He had fallen asleep watching the game with his father, who had since gone upstairs and was now fast asleep in his own room. He got up slowly, stretching the muscles that had been abused by the not so comfortable sofa. Walking to open the door, he glanced at his watch. It was almost one o'clock in the morning.

Don thought someone coming to the house at that hour was strange enough, but he found the identity of the man even more surprising. He looked the new arrival up and down, from the clean cut haircut to the spotless Air Force uniform. The Sergeant looked nervous, like he was on some very important mission. What Don couldn't figure out was why someone from the Air Force would be knocking on the door of the Eppes house, and in the middle of the night, no less.

"Is this the residence of Professor Charles Eppes?" The young Staff Sergeant seemed a little too formal for this hour of the night.

"Yeah, but I'm pretty sure he's asleep. Who are you?" Actually, Don had a nagging suspicion that Charlie was still in the garage working, but it was none of this man's business.

"Staff Sergeant Michael Cruz, US Air Force. I need to speak with him, sir." Staff Sergeant Cruz hesitated for a second before deciding to continue, "This is urgent."

Don was wide awake by now and quite curious about the young man. Just as he was about to ask another question, Charlie entered the living room from the back of the house.

"Michael, I thought I saw your car, why are you up this late?" Charlie took one look at Don and realized Michael's visit would seem rather odd to his brother. He tried to give Don a brief smile to tell him he was sorry, but Don only seemed more perplexed.

"I wanted to get Lorelei's data to you before I clocked out. She seemed really optimistic about this one. God knows we've had enough planes in the sky to give you what you asked for." Michael spoke enthusiastically, handing Charlie the data. Nothing he had said was classified since anyone could see there were planes in the air, but Charlie really didn't feel comfortable with the idea of his family knowing how deep into the military this thing went. They had an annoying tendency of worrying too much.

"Go to sleep, then. I'll work on this and call Lorelei in the morning." Charlie hated working with the team over the phone, but he knew they all needed their space to get this work done. And between Lorelei's many computer screens and his neverending number of blackboards, they simply could not work in the same room.

"Good night, Charlie. Sir." Michael nodded at Don and left the house, leaving Don staring at Charlie and Charlie reading his data, doing his best to ignore Don's look.

Don let himself contemplate the idea he was dreaming this bizarre conversation for a second but then realized this was way too weird to be a dream. If someone had asked him what was the last thing he expected to find on his brother's doorstep at 1 am, a USAF Staff Sergeant would defiantly have made the short list.

"What the…" Don couldn't finish the sentence. "What was that?"

"Just a consulting job and before you ask, I really can't talk about it."

As Charlie turned to walk back to the garage, Don spoke up again. "You're going back to work?"

"I really need to finish this. I'll sleep when I'm done." Charlie knew his brother wouldn't be able to ask him to do otherwise. Don had often skipped nights of sleep when working on a case.

"And when will that be?"

Charlie gave his Don a knowing smile and went back to the garage. Some things were better left unanswered.

Don sighed lightly. If he were a betting man, he would bet Charlie would not get much sleep any time soon. He stalked up the stairs to his old room, thoughts of the comfortable bed pushing away the image of his brother's tired eyes.

1 – 2 – 3 - 5

Please R&R