Disclaimer: I do not own Numb3rs or the characters. No copyright infringement is intended.

A/N: The science in this chapter is from Wikipedia. Many thanks as always to my beta, rhiannondavidson. Thanks, Rhiannon!

Chapter 10

"…a tiny mass of radioactive americium-241, which is a source of alpha radiation. The radiation passes through an ionization chamber. That's an air-filled space between two electrodes. A small, constant current flows between the electrodes. When smoke enters the chamber, it absorbs the alpha particles, which reduces the ionization and interrupts the flow of current, setting off the alarm. And that's why the smoke alarm above us right now contains radioactive material."

Charlie was slouched down on Don's couch with his feet up on the coffee table, staring up at the smoke detector on Don's ceiling. The muted TV in front of them played a late-night sports news recap on ESPN, but neither one of them paid it much attention.

A low, drowsy voice beside him commented, "I can't believe this is how I'm spending a Friday night."

But the affection in his brother's voice softened the complaint enough that Charlie just smiled. Earlier that evening, their father had given them strict instructions to go talk out their differences. So, naturally, they'd talked about every topic under the sun except the one they were supposed to be discussing.

The conversation the entire ride back from the restaurant had centered on their father as they exchanged stories of previous times he had seemingly forgotten that his sons were now adults. Charlie had enjoyed the discussion immensely. As much as he loved his dad, there were definitely moments when he regretted his decision to buy the house. Laughing as he related incidents that had annoyed him at the time, he relished the opportunity to vent to an audience that could truly understand. Plus, it helped to know his older brother occasionally suffered from similar treatment.

By the time they'd reached Don's apartment, Charlie found himself enjoying the truce between them so much that he hated to do anything to disturb it. Apparently, Don was equally reluctant to risk sparking a new argument. Each time Charlie had tentatively raised the issue, Don found a reason to get up from the couch and putter around the apartment.

Asking Don how well he knew the victims got him a curt, "Not well," and then several minutes of Don moving restlessly about the place, picking up dirty dishes and yesterday's newspaper as he muttered something about not expecting guests.

Inquiring if he honestly believed Colby was the leak resulted in a quick, "Nah, not really," and another few minutes of Don hunting around for sweats and a T-shirt for Charlie to sleep in, a towel for him to use, and even a spare toothbrush.

After that, Charlie had relented and changed the subject. He entertained Don with more stories about life with Dad, and as the evening wore on he related some recent events at Cal Sci. Don, in turn, told him about a couple new cases he was working on in addition to the murder investigation. He spoke in general terms, avoiding any specifics, and Charlie resisted the impulse to offer advice. Eventually, they'd run out of things to say and settled into a companionable silence, interrupted occasionally by Charlie's observations about air filters and smoke detectors.

Staring up at the ceiling, thinking about all the things he wanted to say and was afraid to say, a new thought occurred to him. "Hey, did you ever apologize to David? You know, for that night outside The Pantry. You kind of snapped at him…" Charlie let his sentence trail off hoping Don would finish it, but was met with only silence.

Just when he'd concluded Don wasn't going to answer, his brother replied with a quiet, "Nope."

"Why not? You should…"

Don sat up a little and turned to look at him. But his voice remained calm as he explained, "Look, we have a chain of command for a reason. When I give an order in the field, I don't have time to poll everybody on whether or not it's a good idea. The only way I can trust that my team will follow my orders when it counts is to condition them to follow my orders all the time."

When Charlie opened his mouth to comment, Don held up his hand and continued, "That doesn't mean I don't listen to anybody else. You tell me 'hey, I've got an idea' and I'll hear you out. But that's not what David was doing. He wasn't giving me an alternative, he was just complaining 'cause he didn't like my idea. When I first put David and Colby together, you would not believe how much whining I got from the both of them. And I shut them down every time. 'I don't like it' or 'I don't want to' is never gonna win me over. Convince me you have a better plan, but don't ever just sit around and tell me how much my plan sucks."

Settling back down against the couch, he admitted with a self-effacing grin, "I may not always express that well…"

"Ah-ha! See? That's what I'm saying," Charlie gloated. He had to admit, some of what Don had said made sense. But the fact was Don had been out of line to accuse David of not working hard enough; something they both knew was about as far from the truth as you could get.

"Yeah, yeah," Don grumbled as he stood up from the couch. "That's it. I'm going to bed," he commented before ineffectively covering a wide yawn with his hand. "Goodnight, Charlie."

Charlie sat up in surprise as he watched his brother shuffle off toward his bedroom. "Hey! What about… aren't we gonna talk about… you know…"

Barely glancing back, Don assured him with a vague wave, "Later, later."

Watching his brother's retreating back, Charlie felt completely ridiculous as he complained in a quiet voice, "But… I can't go home."

Don stopped short and leaned against the door jamb of his bedroom heavily. Running a hand through his hair in a weary gesture, Don finally turned around to look at him. "Tomorrow, okay? We'll figure it out tomorrow."

The reassuring certainty in his voice was convincing enough for Charlie to nod in agreement and allow his brother to stagger off to bed. But as he sat in the dark living room with only the glow of the TV for company, he began to doubt the truth of Don's statement.