- - - - -

"Agents Sinclair and Granger to see Prisoner #227."

"Have a seat, Mr. Pullman." TJ Pullman eyed them coolly as the guard pushed him into a chair. Colby folded his hands and leaned across the table. "I'm Agent Granger, this is Agent Sinclair. We're with the FBI. " TJ stared over their shoulders at the back wall. Colby continued. "We have a problem. Three bombings in the last couple weeks, and we have reason to believe your gang's behind it. Now I know you have no interest in getting out of here only to find all your buddies have gotten themselves incarcerated just like their boss." TJ scoffed. "Something wrong, Mr. Pullman."

He remained silent, and David took over. "If you can convince us that it's not your gang that's responsible, you may avoid getting a few more years put onto that sentence of yours. You'd stand a chance for parole, and you may even have some friends once you get out of this place. We're only going after the one set of bad guys for now. But in order to do that, TJ, you're going to have to give us some info on who is doing this."

TJ licked his upper lip and continued to stare unblinkingly at the wall. Colby leaned in closer, his voice dropping low. "Do not make the mistake of thinking we won't track these guys down, we will. We're all ready gaining all the knowledge we need from the bombings. But listen, we just came from talking to Jackson Greer." The first sign of interest flickered across TJ's face. "We had real good reason to believe this gang's his. But your incorporation's starting to make me rethink our decision."

David stood up. "Once we know who's behind this gang, it's a piece of cake finding the gang itself."

Colby nodded. "So what's it gonna be, TJ?" There was a split second of consideration on his face, then he seemed to swallow it. "Fine," said Colby. "Agent Sinclair, would you give Agent Eppes a call? Let him know we have our man."

David opened his phone, and the two started leaving the room. Suddenly, TJ spoke up. "What kind of evidence you lookin' for on Greer?"

Colby turned around casually, looking at the ceiling as though for inspiration. "Ah, you know…names, locations, any dirt you got, TJ."

TJ cocked his head to the side and, still trying to look nonchalant, nodded. "A'ight. You dudes got a pen?"

- - - - -

David shut the door behind the two of them, and gave Colby raised eyebrows. Colby laughed. "I can't believe he went for the, 'call it in, we have our man' thing. I mean, it's a classic, right? Doesn't this guy watch TV?" David smothered a laugh and Colby put his hands in his pockets. "So what now?"

"Now?" David smirked at him. "Now we go talk to Jackson Greer."

- - - - -

"Negative on the grocery store and restaurant front," Megan sighed, pushing away from her computer.

Don nodded. "How about CalSci?"

"Same results as the cursory check we made on the scene; no one's seen Greer or Pullman. It stinks, that scratches revenge off the list." She shook her head, spinning one of the crime photos around. "Two people killed and six hospitalized at the grocery store and five hospitalized at the restaurant. All low-casualty attacks on buildings with no common denominators."

"Yeah. Charlie's working something, though, some…hive theory, gang behavioral patterns…I don't know what the heck he's doing now, actually."

"Whatever's Charlie-speak for a mathematical answer to our dead-end."

Don laughed. "I probably should go check on him, he's been scribbling away in there for over an hour."

Megan glanced up at him. "You look kind of stressed, Agent Eppes."

He growled under his breath, calling it quits on the files he'd been pouring over. "I just…can't help but think there's another bomb out there waiting to go off. I hate having no leads to follow." Megan just gave him a smile, a nod, then turned back to her computer. Don got up and opened the glass door, entering the briefing room which was now littered with Charlie's notes.

"Hey, how's it going?"

Charlie worked furiously at the whiteboard, not looking up when Don entered. "Uh…" there was a long pause before he mumbled distractedly, "yeah, working on it."

"Wouldn't you feel better taking this to your office at the school?"

Again, there was no response at first. Then, "No I don't…too much distraction."

Don nodded, catching on. "Right, right the bomb. You know- no one was hurt, Charlie, the hall was completely empty."

"Yeah, yeah I know. I just-" Charlie's marker hovered uncertainly over the whiteboard and he stared down at his shoes. "I uh…can't. I can't work with investigators on campus, and smoke in the air, and everybody talking about how…how people could have died." He shook his head and started writing frantically again.

Don chewed his lip a moment then nodded. "Well listen…don't push yourself too hard."

"You need this, they- the FBI needs this."

"I know, but just this morning you were bedridden with a fever."

"I'm fine."

"Well- I'm glad." Don thumped him on the back. "Just promise you won't overdo it, okay? If you're getting tired, just let me know." Charlie gave a curt nod and went right on writing.

Don stood and watched for maybe five minutes…

F(x, y, y', y", …, yn-1) y(n)

Yn : y (n-1)

y' F(y,x)

Somewhere around the fifth line of y's, x's and parentheses, Don slipped quietly from the room and left his brother to his work.

- - - - -

Colby looked irritated when he David come walking out of the elevator an hour later. "Uh-oh," Megan said when they came around the corner. "You look riled, Granger. How'd the interrogation go?"

David dropped a stack of paper on the desk. Don raised his eyebrows. "You got official statements? From which one?"

"Both," said David. "TJ gave us several tip-offs against Jackson Greer."

"And Greer?"

"Gave us plenty of evidence against TJ."

Don nodded. "Even if they're both wild good chases, we can probably bet that each statement is a model of where they don't want us to go, right?"

"Yeah," Megan agreed, "why would they send us anywhere near where their gangs are really hiding out when they've got this golden opportunity to point us in the opposite direction."

"So long as we account for the possibility that they're a little smarter than that, this can be helpful." Don nodded at them. "Good work, guys."

Colby scowled. "Gotta tell you Don, those two are sick. You should have heard them bragging their past illegal exploits with those smug smiles on their faces. It's disgusting, I wouldn't be shocked if they both turned out to be our guys."

"Hey, don't let it bug you," Don told him. "We'll nail these guys. Charlie's got some new algorithm cooking now, so it's just a matter of time." He went to the briefing room and swung the door open, poking his head inside. "Hey, Charlie? How's it coming."

"Uh…" Charlie stood back, examining his work. "Okay. Okay…what've you got there?"

"Just some statements from our boys in the state pen."

"Greer and Pullman?" Charlie took the stacks of paper and started breezing over them.

"Does that fit into your…your behavioral theory thing?"

"Yeah…yeah, actually this helps a lot. Give me…an hour. I'll run all this data through, get you a detailed model."

"Can you give us anything to work on from what you have so far?"

Charlie looked at the whiteboard hesitantly. "Well I had it narrowed down to two spectrums to check: One for Greer's guys, one for Pullman's. I'm working the two separately until we know which one we're after."

"All right."

"But with this new data, I could get you something more accurate."

"Charlie, for all we know there's another guy out there with a bomb, just waiting to go off. We need a pattern, even a springboard." He smiled apologetically. "I'll take whatever you got."

- - - - -

"Gang Theory, Hive Mind, Groupthink, all different ways to explain the same concept; that people and their behavior as a group can be analyzed with mathematics, and almost completely deductive reasoning. I could…" Charlie looked hesitantly at Don. "You want me to do the traffic analogy again, or…"

Megan waved a hand. "We don't need to know how it works, Charlie, just what it does."

Charlie nodded, picking up speed. "Okay. Well, I read through Jackson Greer's and TJ Pullman's profiles, their backgrounds, their parents, friends, hangouts, homes. The more information I can run through this algorithm, the more exact my estimates."

"You turn humans into equations?" Colby glanced around. "I'm almost afraid to ask…is that even possible?"

"Involved, time-consuming and not 100 exact, but possible. Yes."

"Wait, what do you mean it's not exact?" Don pointed to the graphs taped to the whiteboard. "You said you were pinpointing a location, that sounds pretty exact to me."

"Calculating for a vicinity, yes, but not a location. I could narrow that vicinity even more if I had time to process these statements, but you said you wanted this now."

"Yeah, no. This is good, anything you got it is good, Charlie."

Charlie nodded, and grabbed a map off the table, unrolling it. "I just got this printed up…let me just…" he turned it this way and that, then grabbed a notebook, flipping quickly through it. "Just a minute, I think I…yeah, the directional diagram wasn't correctly split. Well, I can guesstimate." He taped it to the whiteboard, and pointed to what looked like a target whose rings got darker and darker towards the center. "I've mapped according to likelihood. The darkest rings are more specific, but less likely."

"Less likely how?" David asked.

"Well it's too specific. But, it's your best chance in making an actual bust. See, these largest rings cover the greater part of southern Los Angeles, so the likelihood is greater. The narrower the field, the more specific and the more room for error."

"But we can't kick down doors all through southern LA," Don added.

"Exactly. Now the computer messed up somehow, I don't have the coordinates I added for Pullman, but I mapped out his local as well. And guess what I found." Charlie grabbed a black marker and made three rough circles. He thumped the maker on the innermost circle.

Don leaned forward. "They intersect." Charlie pointed at him in a 'give him a prize' sort of way. "So what, are you saying that these guys…that Pullman and Greer are working together?"

"I'm not making any assumptions, that's your department," Charlie said, capping the marker. "But I'll tell you this: Until I factor in those official statements you gave me, my approximations put the gang of both Pullman and Greer in this vicinity possibly on an early weekday. Also, I calculated as best I could their temperaments and preferences and think you're looking at organization."

"Meaning discreet meetings, crowded buildings, busy parks and whatnot…" Don went to the whiteboard, studying the map. "What, right here on Wilshire Boulevard?" Charlie nodded. "So what's here besides us."

Colby shook his head. "Let's see, uh…Academy of Arts and Technology, Institute of Architecture and Design, CEI…lot of institutes, a lot of colleges."

"Yeah, but how many of them admit visitors?" David pointed out. "It's got to be somewhere with a steady flow of visitors. Preferably free entry, to avoid security."

Don's eyes flicked over the map, his mind working. Then he thumped the board suddenly. "The LA Museum of Art." Megan spun around to her computer as he kept talking, his voice speeding up. "Free admission, low security, high attendance-"

"Here it is," said Megan, pointing to her monitor. "Open on Tuesdays noon to 8pm."

Don looked down at his watch. "Okay, so we assume they're going to aim for the afternoon rush…we need to get a move-on."

David stood up. "I'll send the museum a photo of Greer and Pullman, let them run it by the staff. Maybe we'll get lucky."

"Yeah, go ahead. Colby, get the team ready. Megan come with me, we need to get a copy of that building's blueprints, look for meeting spots and escape routes."

Charlie was looking uncomfortable. As the busy room began to empty, he came up behind Don, grabbing his shoulder. "Hey umn…how do you know they'll be there today? I mean-"

"Well you said it Charlie, an early weekday, right? Museum's closed on Wednesdays, so unless it was yesterday, it's got to be today."

"Yes, but I'm not- I can't be sure about the early weekday thing, it was an approximation."

"Charlie, around here we have to act on approximations or we never catch the bad guys." He smiled and gave Charlie a whack on the shoulder. "Hey, don't worry. I trust your judgment. Look, why don't you go home and get some sleep. You and Dad can, I dunno, watch TV or do crosswords or something. Something to relax, okay?" He stopped at the expression that had come across his brother's face. "What's wrong?"

"Dad." Charlie ran his hands through his hair. "I told him I was getting lunch with Larry, then I thought of the gang theory application, and…oh man, I promised him I wasn't going to come down here today."

"What- Charlie, what were thinking? Dad's gonna kill me, he's probably going crazy wondering where you are."

"No, he probably knows exactly where I am," Charlie said, looking like that made him feel even worse. "Oh man, I left- I left my cell in the car."

"'kay, Charlie, you know what? Call Dad, go home."

"But I was going comprise those statements-"

"Hey, you gave us more than enough to go on, okay? Get some sleep, I'll make copies of the statements and come over later, give you an update. Now- go on, get out of here."

- - - - -

Don walked brusquely through the front door and made a b-line for the front desk. "Excuse me ma'am, Don Eppes, FBI." He flipped his badge open for the her to see. "I need to speak to your manager right away."

"Agent Eppes!" A tall man in a black suit came striding up and shook Don's hand firmly. "James Walker, I'm the head of security. I spoke to the board and some of your people on the phone. They tell me you think there is a terrorist meeting being planned in our building?"

"Not precisely terrorists, Mr. Walker, but a gang who has been demonstrating terrorist behavior. I would like your permission to send Agent Reeves to the observation room. My team and I will survey the upper and lower levels, I would appreciate it if you could tell your people to stay on the mid-level by the entrance."

Mr. Walker seemed a tad overwhelmed by all this information, but kept his cool. "Of course, I'll inform them immediately. This way, Agent Reeves." Megan left with him, and Don turned to address the rest of the team.

"Colby you take Franklin and Hummel downstairs, search all the lower floors, work your way to the middle. Keep close to the exits. Hansen, Podolsky, come with me. Let's move!"

The pounding of boots echoed through the corridors as they went up flight after flight. Finally, they reached the top and burst through the door. Everyone slid instantly into stealth mode, guns stowed in their belts, trying to look nonchalant to avoid a panic. They slipped quietly through hall after silent hall, each lined with paintings and plaques. Every time they reached a small huddle of people, Don would say quietly, "FBI, nothing to worry about. Routine inspection."

"Don," Megan's voice made his earpiece vibrate. "Possible suspects in the…Jacques-Loise David exhibit, around the next corner. Proceed with caution."

"Copy." They turned the corner to an open room with white walls and blue carpet. In the center of the room stood three armchairs and a couch. Don hesitated as four young men looked up. One was standing, the rest were seated comfortably in the armchairs and seemed to have just come out of an engrossed conversation. Don reached for his badge, "FBI, gentlemen-" and they bolted.

"Move in! Move in!" Don shouted, pulling out his gun. "Colby, first floor, first floor, west side, copy!"

"Copy," Colby's voice came in. "Heading to the stairwell."

"Take the east stairwell, head them off," Don ordered, running flat-out after the four men. Podolsky split off to the side, cutting through a small exhibit to the left, and heading one of the men off. He lunged and took the man down with him. "FBI! FBI, stop resisting!" he shouted, pulling out his cuffs.

"Good work, wait for backup," Don told him quickly as he and Hansen continued to peruse the other three.

Suddenly a door up ahead of all of them burst open and Colby and his team came pounding down the hallway. Two of the suspects went left, the third went right. Unfortunately, Colby, Franklin and Hummel all went left. They tackled two of them to the floor, but by the time Don had caught up to Colby and his team, the third was almost to the end of the hallway. Don looked up just in time to see a figure vanish into the shadows as the door slammed shut. "Megan, you have eyes on the stairs?"

"That's negative, Don, no surveillance on the staircases."

"Then we just lost one of our guys."

"Can you give me a description to pass along to the boys downstairs?"

Don shook his head dryly. "Young man in a coat and tie. Medium height, weight…probably would blend well with one of the twenty college tours here today."

Megan's voice reflected the sarcasm Don was feeling. "Copy that."

He turned, out of breath, and nodded appreciatively at Colby. "Thanks, that was fast." Colby gave a thumbs-up, too winded to respond. Don nodded to the two suspects. "Let's go have a chat about Jackson and TJ, guys."

- - - - -

"Dad?" Charlie dropped his keys on the kitchen counter and draped his coat over one of the chairs. "Dad, you here?"

"Living room," came a distant voice.

Charlie strolled into the living room, hesitant. "Hey."

Alan looked up from his newspaper. "Hi."

"I uh…had four missed calls from home. Sorry, I left my…my phone in the car."

"So how's Don doing."

Charlie bit his lip. "Huh…yeah, I figured you'd…figure that out."

"Listen, Charlie. I'm not angry." Charlie looked at him, expectant. "I just- I know you get stressed when you can't do the things you normally do. As long as you're sick, you won't be able to do those things, and until you let your body get some real rest, you're going to stay sick." He ruffled his paper. "I'm just trying to take care of you."

"I know you are," Charlie said, crossing to the couch, and lying down. "I'm sorry I didn't let you know where I was."

"I knew where you were."

"Yeah," Charlie laid his arm over his forehead, shutting his eyes. "But I'm sorry I didn't tell you."

"Well, apology accepted." Charlie heard him stand up. "Now, I'm going to make you some chicken soup."

"Dad-" He sat up quickly. "I know you're just looking out for me, but please, please, don't make me eat any more chicken soup."

A smile twitched at the corner of Alan's mouth. "Sandwich?"

Charlie smiled his relief. "Yes please."

"Bologna? Turkey?"

"Turkey's good."

"Coming up."

Charlie lay for awhile, listening to dishes clink in the kitchen. "Don's working on a case that involves that theory on behavioral studies I was working on awhile back," he called.

"Yeah? How's it coming?"

"Good." He wrinkled his forehead. "I think. I don't know, it seems so- imprecise. Even with my theory applied to it, all the variables analyzed, there's so much guesswork, so many hunches."

"Well, Charlie," Alan's voice came closer as he returned to the living room, two plates in his hands. "You can't really expect to fully analyze something as incredibly complicated as human beings. There's always going to be guesswork, to some extent." He sat back down on his chair. "Now is this the lecture you're giving at CalSci?"

"Actually, that one was on using mathematics to create unbreakable passwords capable of rotating as a means to fortify computer security," he said, sitting up and plucking lint off his t-shirt.

"Sure, why not." Alan smiled. "So have they rescheduled that for you yet?"

"Oh, uh…you know, I'm not sure."

"You're not?"

"No," Charlie reached for his sandwich. "But I'm sure they'll let me know." He blinked irritably. "Not as though it matters, since I seem to have misplaced my calendar."

His father seemed to find that amusing. "How'd you do that."

"Hey," Charlie pointed at him. "It's not funny, I had to get Amita to help me redraft my whole schedule."

"What, you mean-" Alan reached into his coat pocket and pulled out a brown, leather planner. "This schedule?"

Charlie seemed put out. "Where'd you find that…"

"Buried downstairs in your mad science lab, go figure."

Charlie smiled a little, taking the planner. "I'm on the cusp of a very useful, practical step in computer security, Father."

"And you're also a genuine slob, my son." Charlie gave him a 'touché' expression and started into his lunch. "If your breakthrough's so important, then why haven't they rescheduled it, yet? I heard this was a big deal to CalSci."

"It is, it's just…" Charlie shrugged in what he hoped was a causal way. "You know…rescheduling takes time, that's all."

Alan eyed him for a moment, then seemed to drop it. "Well I wouldn't stress over this whole behavior theory thing too much. I'm sure whatever you can do to help Don is well appreciated and very useful."

"Let's hope so."

They ate their sandwiches in silence. Then Charlie smiled to himself, rocking back and forth a little. Alan raised his eyebrows. "What is it?"

"I was just thinking, you know…I'm still not quite adjusted to this idea of practical application of concepts. I mean, I teach applied mathematics, and still it boggles me how such information can be used wide-scale like it was when I worked with the NSA, or even more so now, with the FBI."

"I don't follow…"

"Well, we use math for everything, really. But application of this magnitude, it just, I don't know…it's a good feeling. When mathematics are applied to crime- it's possible with this theory, my theory, I could…" He shook his head, fiddling with the edge of his plate. "We could have a obvious drop in crime activity."

"You really think you can do all that with this one idea?"

"Not me. And the concept of behavioral studies has been around for ions, in one form or another. But with the algorithm that I have made, specifically tailored to LA crime, we could be tracking these people down. Making those responsible for crime start paying for it. And it's all thanks to Don, opening that window for me, allowing me to work with the FBI."

Alan nodded slowly. "This is pretty heavy stuff, Charlie."

Charlie smiled, unperturbed. "Yeah. I guess it is."

- - - - -