A/N Written for The Room Forum's 2019 Pi Day Challenge. Thank you, VStarTraveler, for the challenge. Still unbeta'ed, but finished in Hawaiian time.

2019-03-25 Edited again, but still unbeta'ed.

2019-03-27 Fixed several remaining mistakes; thank you darkaccalia520!

Like π

Megan stared at the remains of the letterbox in front of her. Blood and splinters littered the ground around her.

"Clever way to build a trap," Colby said, rising from his crouched position. "What does this make? The fourth explosion in the last three hours?"

She nodded. "A physician, a bank consultant, a car dealer and now a mailman." The house used to be well-kept and tidy. But now the front windows were shattered, having been blown apart in the explosion.

"It's a miracle that he is even alive," Colby said, following her gaze. "Four self-made bombs. I guess we now need to assume that this is the work of a serial bomber."

Megan pocketed her sunglasses. "You said it yourself, these were cleverly laid traps. Whoever built these bombs was a patient man with a lot of swallowed anger. It took years to reach the boiling point that leads to this violence."

"Meaning our guy is going all the way." Colby sighed. "Guess we better find the common link between our victims. Fast." He glanced over his shoulder with a questioning look. "Charlie?"

Agent Megan Reeves nodded. "Don was already on his way to him as we got the call about another bomb."

"I'd propose to issue a public warning not to go to your letterbox, except we had explosive devices hidden beneath a car, the doormat and a package left in front of the door." Agent Colby Granger crossed his arms. "There is no single pattern."

She opened her mouth to give a reply as she spotted Don's SUV. Crossing the street, Megan reached the car just as he jumped out. "Our victim number four is a mailman, divorced, no priors and his neighbors have only good things to say about him." She made her report without wasting precious time.

Don chewed his gum. "Did he survive?" He glanced to her, but then his gaze returned to a nearby house.

"He was alive when they took him to hospital, but it's not clear if he is going to survive." Megan followed his gaze, puzzled. "Charlie?"

"Is working on it," Don reported and narrowed his eyes. "You see it, too?"

Scanning her environment again, Megan finally spotted it. Slowly, she nodded. "Second house to the left, gray, old and a parked car, but nobody is looking outside." Megan adjusted her vest and gun. All other neighbors were glued to their windows, not really hidden behind a curtain or they had taken their cars and fled the violence that had suddenly erupted in their neighborhood. But not this house.

David hurried over with a notebook in his hand. Worry was etched on his face. This time, they had the power to prevent another victim and not just picking up the pieces. But only if they could stop the bomber in time.

"We should take a look at the house," Megan voiced her agreement and shifted to allow David to enter the discussion.

"That we should," David rushed out his words. "The guy living over there is Simon Ire." He pointed to the gray building. "He was supposed to be evicted today and blamed our victim for the trouble with his landlord."

Don nodded, checked his watch and started to move. "Connection to any of the other the victims?" The air above the pavement flickered in the oppressive midday heat.

David shrugged. "I literally just learned his name. But maybe, on contrary to our victim, this Simon Ire was a choleric and estranged with everybody," he reported while his hands smoothed over his jacket, verifying that he was as much protected as possible by his vest.

Together, they crossed the street. The gate was well locked. His finger hovered above the bell as Don suddenly hesitated. "Choleric, you said?" He tilted his head and glanced to David out of the corner of his eyes.

David, positioned behind him, nodded. "Nobody had to say anything good about him."

Don's eyes shifted to Megan. "And he was supposed to be evicted today?"

Another nod from David confirmed it.

"It would fit," Megan answered the unvoiced question from her boss. "The eviction notice could act as the final trigger to implement a plan. It could be our guy."

Don pulled his hand back. "Let's get bomb squad to check it out and run a check on him."

"And?" Megan paced the conference room as David finally arrived. She had been the first to return to the office to start with the background check. Her results were a worrisome amount of files and complaints.

"Good thing that we let the bomb squad deal with it. There were at least three explosive devices hidden there." David dropped into the nearest chair, rubbing his hand across his face. The exhaustion was almost palpable in the air.

"They were meant for whoever dared to enter his house." Megan stared at the photo on the screen. A man in his fifties stared back with dark hair, no stubble and cold eyes. "It fit the profile. What doesn't fit the profile is that he is missing. He should be out justifying his actions."

"He's not missing," David said. "He's dead. We found his body in the garage."

Surprised, Megan blinked at David. "How did he die?"

"The coroner thinks it could be poison, based on the pictures of his face. Either way, we've found a suicide note." He held out a bagged piece of paper.

Carefully, Megan accepted the evidence and inspected the note. It was written with a strong pen stroke but clear letters. "He really had planned all of this." Content-wise, it wasn't anything new or surprising. He rambled about injustice and how he would go out and take everybody with him who had done him wrong. It was almost an active shooter scenario except the shooter was already dead and his killings were happening in slow motion by carefully planted bombs.

The elevator dinged and Don rushed out with a deep frown on his face. He had come from upstairs. No doubt that ADIC Wright had asked for a fast and informal briefing. "Does it say who he wants to kill?" Don asked without pausing, indicating the suicide note with his chin. Apparently, he had already been informed.

Megan narrowed her eyes. If he knew about the suicide, his stressed body language had to have another reason. "No," she said with a shake of her head, "but I guess we have another explosion?"

Don nodded. "Currently, we get called whenever something blows up, even if it's just a century old gas line. But over in Venice, they found an explosive device similar to ours that almost killed a woman."

"Name?"

"Helen Norton," Don said. "Does Charlie have anything for us?" Don's brother Charlie wasn't only a world-famous mathematician but also an important consult for their cases whenever they needed a fast way to filter lists and find unique connections.

David frowned and grabbed a file, searching for something.

"Not yet," Megan answered. "But he thinks he can get some fast results to give a starting point. I gave him every name that came up in court documents or other files in connection with Simon Ire." She pointed to a table with several piles.

Don's eyes widened at the sheer amount of paperwork. "Let's hope Charlie can narrow it down." Megan also had been surprised to find so much in so little time.

"Where's Colby?"

"Still at the crime scene. He's looking for some hints in Ire's house," David reported while he still shifted through some papers. "But according to some bills we've found, we have to assume at least another bomb." He glanced to Don before he refocused on the file in front of him.

"Great," Don murmured. He glanced at his watch. "We have to stop a killer who is already dead but his victims could still be saved."

"Got it," David interrupted. "The Venice explosion is ours." Holding up a file, he explained: "Helen Norton was Simon Ire's landlord."

Don clicked his fingers. "Call Charlie and give him the newest data, I'll try to get more agents to call every single person in his files and warn them." He rushed to the door, his cell already in his hand. "And David?" He turned around and pointed at Agent David Sinclair. "Write down all names and phone numbers we have already found." Then his call connected, and he left the room, talking to whoever he had called.

Nodding, David climbed to his feet and left the conference room, while Megan grabbed the land line and dialed their mathematician's phone number out of memory. "Charlie?"

"Yes, I've got something for you." He sounded excited and hope blossomed in her heart. Maybe they would be fast enough and could warn the most endangered first. "That's great."

"I think I know who's the next target. He has the highest probability — twenty-three percent. Mind you, it's just a preliminary result but Don stressed how important every hint is." In the background, cars and the sound of people could be heard. "I'm on my way."

"That's great." If Charlie worked in the FBI office, they could save even more time. "And who-"

Suddenly, a startled shout came through the tiny loudspeaker. "Charlie?" Squealing tires and the sound of something crashing followed.

Megan jumped up. "Charlie!" she demanded, urgency making her voice stronger. "What's going on!"

A horrible noise, as if something or somebody was hitting the ground, came out of the loudspeaker, distorted and strange. "Charlie!" Megan glanced across the office, but nobody looked her way.

Finally, she heard a soft sound like a human voice. "... like pi," Charlie said. But his voice was small and almost breathless. "You need to -"

The line went dead.

Megan barely waited for the car to stop rolling before she jumped out. The campus police had already cordoned off the area. She didn't even need her id, being a familiar face on campus allowed her through without any hassle.

A red Ford in the middle of the street seemed to be the center of attention. Two young women were leaning against it with tears streaming down their faces.

"It was an accident," the detective stated before Megan could open her mouth. "Every witness and the driver herself are consistent in their accounts. The driver had been arguing with her passenger and Professor Eppes hadn't looked before he crossed the parking lot."

Megan pressed her lips together. "Where's -"

"The ambulance has already taken him to the hospital. He has sustained some injuries, but nothing life-threatening, but he was knocked out." The detective continued to talk, taking the chance to say everything necessary before Megan could barrage him with questions.

Allowing herself to take a deep breath at the confirmation that Charlie was alive, Megan refocused her attention to her next problem. "What hospital? I need to talk to him. It's urgent." A car accident was no joke but hopefully he was just bruised and his cell phone had been broken, so he hadn't been able to call back. Then she would get away with driving here without informing Don. If Charlie was hurt more seriously, she didn't know what explosion she should be worried about — Don's reaction or the real bomb.

"Good Samaritan Hospital."

"Thank you." Megan turned away. Either way, it was time to inform some people.

"Agent Reeves?"

"Yes?" Megan turned back.

"I don't think you can talk to him. It looks like he has a complicated forearm fracture or maybe it's his wrist," he explained. With his right hand, he offered a notebook and a rolled map. "Professor Eppes had carried these things in his hands." He paused. "My mother is a surgeon. He's going in surgery as fast as possible to prevent nerve damage."

Megan pressed her lips together. "He had figured out where our last bomb is hidden. I'm sure that he has already told them that." She grabbed the offered items. "I need this information."

The detective shook his head. "Have it your way." Then he turned away, going back to his work, leaving Megan running through the crowd with her cell in her hand. David would be faster. But Megan knew that the detective was right. Charlie's own health had priority. Hopefully, he had told somebody more than just like pi.

After a short hesitation, she changed direction. If Charlie was unable to help, there was another chance she had. The call to Don had to wait another minute.

"Amita," Megan held out her hand to stop the professor from rushing out of Charlie's office. "Do you know what Charlie had figured out?" Larry Fleinhardt, their third professor, was right behind Amita.

"I need to go," Amita moved around, never stilling. The worry for her boyfriend was written all over her face. "Charlie is in the hospital and I need -"

"Amita," Megan stopped her again. This time she lowered her voice and made a calming motion. "Relax. His father Alan and David are on their way. Charlie is in good hands. But he told us that he had figured out where the last bomb is. I need to know."

"Didn't he tell you?" Larry crossed his arms. "I know that he stormed out of here, smiling like he had hit the jackpot and dialing your number."

Megan glanced to her boyfriend. Hugging him and feeling his heartbeat would help her now to deal with her emotions, but she had a job to do. Her own comfort had to wait. "I couldn't understand his words. Just 'like pi', that's the only thing I could make out."

Amita glanced to the boards. "I can't find any equation that uses pi. I don't think he used pi at all. This," she indicated to the columns of numbers on the blackboards with her chin, "calls for a filter approach and not pi."

"I cannot imagine a situation where Charles would use pi to narrow down a list of potential targets." Larry stepped up to Amita, agreeing with her verbally and supporting her with his presence. Charlie was Amita's boyfriend, but Larry had been his friend and mentor longer.

"So, we got nothing?" Megan bit her lips. They needed to narrow down the names to get a warning out in time. No matter how many agents Don could get, they had dozens men and women to call and explain the situation, warning them about an explosive device that could be hidden beneath their doormat.

"Charlie is the only one who knows the solution."

Megan sighed. "And Charlie-" Her cell phone rang. After a quick glance to the id, she snapped it open. "David?"

"Charlie is mostly fine, but in surgery. Alan is here," David reported. His voice sounded weary and Megan's hope fell. Her shoulders sagged down.

"Did you talk-"

"I could talk to him for a minute. But between the knock on the head, the pain and the shock, he just repeated what he had told you — like pi," David said.

Megan pinched the bridge of her nose. "How long-?"

"Until he properly wakes up and can hopefully explain to us what he had figured out moments before he was hit by a car?" David recounted every obstacle. Her hope diminished even more. "Several hours."

Megan closed her phone. They needed to figure out what Charlie's clue meant. They just had to figure it out.

Megan watched Don through the window of the conference room. She was sure that it was only his sense of duty, and maybe his fear about losing control, that kept Don in the office. But his muscles were locked tight. He paced the office more like a tiger ready to jump than the lead agent on a case.

Next to her, Megan heard how David and Colby shifted through files and collected evidence.

If Don didn't issue orders or directed one of the new agents, he had his cell pressed against his hear. Finally, a call seemed to be good news and his tense muscles relaxed. He entered the conference room with a smile, and Megan breathed out.

"Charlie is out of surgery. Everything went well, but it's going to take some time until he is awake enough," he reported. "So, we still need to figure out what he had meant with his -" He raised his hand and stared at Megan.

"Like pi," she repeated dutifully. She hadn't thought about anything else except these few seconds on the phone with Charlie. "That's what he had said." Had she missed a clue? Had he told her maybe a name or address?

Don sighed. "Like pi. Figures." He rubbed across his face. "So, any ideas?"

"Charlie had carried a map. Amita reported that he had been working on something, looked at the map and then ran off," Megan explained.

"But he hadn't told her what he had discovered?" Don fell down in a chair and pinched the bridge of his nose. "He should have told her."

Megan could only guess the amount of pressure he felt. "She's trying to follow his calculations and hopefully comes to the same conclusion." Like a broken record, she was repeating the same thing over and over again. It had been a struggle to convince Amita and Larry to keep working and not spending their time in a hospital waiting room doing nothing but waiting. But in the end, Charlie and Don weren't the only ones with a sense of duty, a sense of right and wrong.

"What else?" Don picked up a pen and started to play with it.

"We used the map and tried to find pi," David said. "But the locations of the bombs don't have anything to do with a circle."

"We checked addresses and whether they fit — nobody of his listed enemies live in or near a 3.14." Colby pushed his pile away. "We even checked if somebody is called Pi or his name starts with Pi."

"But there's only a Picard who has moved to Indiana almost ten years ago," David finished the explanation without missing a beat. "I'm not sure why somebody gone for so long is still in Ire's notes."

Megan wasn't surprised about the long time frame. But now wasn't the time to refine her profile. "Larry checked whether the distance between the house of Simon Ire and his victims is pi or related to pi, but he can't spot a pattern."

"Alright, I'm done," Liz announced as she came into the room, interrupting their discussion. "I've checked everyone's birth date." She shock her head. "But got nothing. Two were born on March 14th but one died already last year in a climbing accident and the other one lives abroad."

"Any sign of a letter bomb?"

"No, as far as we can tell," Colby said, "he had only built pipe bombs. Easy to build, easy to detonate but also easily detected. His best bet was the normal behavior of his unsuspecting victims."

"You sure that Charlie has said 'like pi'?" Don glanced at his watch before he looked over to Megan.

"Positive," Megan responded. Somehow she managed to not let the anger bleed into her voice.

"Maybe he didn't mean pi but pie?" Liz proposed and rested her hip against the table. "It's impossible to distinguish without context."

"But with Charlie math is the context," David argued.

"Maybe not." Don crossed his arms. "Go check it out — maybe he had a dispute with a baker or one of his potential targets lives near a bakery. It's possible if it's something that he has spotted on the map."

Liz arched an eyebrow.

"I know that checking this is enough work for weeks," Don said frustrated, "but we don't have much choice until Charlie wakes up and explains us properly what he has found out. Until then, we have to do our best, trying to find the last bomb before we have another victim."

Liz nodded and pushed away from the table. Determined, she stalked to the door of the conference room and slipped out.

"The press is informed. Hopefully, everybody is now more careful," David added.

"Anything else?"

The silence to Don's question was answer enough.

Megan kept Don in her line of sight. He gazed into space, but with a glare that could have killed. She could guess what he was thinking about. Finally, she had enough and stalked over. "Is he awake yet? Can Charlie tell us something now?"

Don startled. Then he shook his head. "No."

"No?" Megan crossed her arms. "How do you know if you don't call."

"I don't need to." He stared at her with an annoyed expression. "I called a minute ago and three minutes before that. I don't think my father is going to accept another call."

Megan nodded. Pulling over a chair, she sat down in front of Don. "We're running out of time. People are getting home from work and then -"

He glanced to her. "I know. But there's nothing else we could do." He rose. "We have a public warning out for everybody who ever had contact with Simon Ire. We are calling whoever we find in his files. I have half the office running down every lead and the other half trying to figure out the shortcut Charlie had found. I have agents in Ire's house trying to uncover another clue and other agents checking where he had been the last few days." Deep creases on his forehead and his hanging shoulder reminded Megan of Atlas, the man who carried the world on his shoulders.

"You're right, we do everything we can." She paused. "So, how is Charlie? If you have already called your father, Alan could tell you something, right?"

A relieved smile flickered across his face. "The docs say he is going to be fine as long as there's no infection."

Megan leaned forward, her elbows resting on her knees. "Don, you are our best shot trying to figure out what Charlie could have seen."

Don snorted. "He may be my brother, but I sure don't think like him."

"You don't need to think like him," Megan talked over his protest, "you just need to know him. Whether you want or not, you know him really well — that's a side effect of growing up together and being siblings. If you spend enough time with somebody, you learn to know his behavior and actions just by being around. And besides, I'm pretty sure that you experienced the same thing I did — people took your kinship to Charlie as an invitation to tell you everything you didn't want to know. "

A painful expression crossed Don's face before he settled on a more neutral expression. "And?"

"What do you think Charlie would try to tell us with 'like pi'? Not what 'like pi' could mean, but what Charlie could try to say with it?" For a moment, Megan assumed Don would refuse to play her game, but then he sat back down.

"For Charlie everything is math, but he tried to tell you something. And if it's not something obvious then I don't think he would try to explain complicated mathematical ideas to you."

"So, pie as in food? Not math?"

Don screwed up his face. "In time of need, Charlie is not one to turn to food."

"Except when he needs my food for one of his analogies." She smirked.

"Except then." He gave her a quick smile. "But again, he is a teacher and wouldn't ask too much of you." Don climbed to his feet and started to pace. "He was talking to you. It was a message for you." He lowered his voice as if he was talking to himself.

"And had a map in his hand with the locations marked," Megan said and used the same soft voice.

"Pi," Don murmured. "He tried to tell you something about pi." Suddenly, he straightened. "Of course," he exclaimed and hurried over to the conference room.

Megan jumped up and ran after him. Again, she was reminded of people running off with a new thought without sharing it. Colby stepped back to make room for Don who rushed to the nearest table. David put down his phone.

"If Charlie thinks about pi," Don explained, "he doesn't write it like 'pi' or 'pie'." He cleared the table and put down the map. "He always uses the Greek letter: π."

Megan frowned and Colby raised an eyebrow.

Grabbing a red pencil, Don started to connect the locations — drawing a perfect π on the map.

"Pi!" Now Megan could see the pattern on the map.

"Whatever he saw as a connection, it's located somewhere on this line," Don said while his finger tracked the line. He looked to Megan. "And that was the easiest hint he could give you."

"So, what? We were trying to use math and Charlie just wanted us to draw a Greek letter on his map?" Colby sounded slightly betrayed.

"He knew what we could or couldn't do, and higher mathematics isn't one of our specialties." David rationalized and went over to their files about legal battles Simon Ire had been involved.

"The left pile," Megan said. "I took the liberty to sort them by priority."

"Priority?"

"He directed his cold anger against powerful people who he felt were unjust to him. If he could express his anger in another way, like a complaint and was validated in his feelings, it didn't simmer until it exploded."

"Literally," Colby said and accepted the resulting looks with a raised head. "What? It's true."

"Alright." Don clapped his hands together. "You go through the files, and we are driving over there. Then we will be already in the right area." He grabbed his jacket and tapped Colby on the shoulder. To Megan, he added, "Tell the bomb squad to meet us there. We're going to need them."

Megan grabbed the phone. With her other hand she took the next file, paging through it, hoping to spot a matching address. The adrenaline pumped through her veins, providing much-needed energy. This time they would be fast enough.

"Hi Charlie," Megan jumped up to greet their visitor.

Just a week ago, they had raced against time to find the last bomb while Charlie had been in surgery. He had well recovered from being hit by a car and the actual defusing of the bomb had been rather anticlimactic. After they had identified the office of a lawyer right at the intersection, Don and Colby had cleared the building, called again the lawyer who had been already warned and had stayed home. Then they just needed to wait for the bomb squad who found and defused the explosive device, recovering the last unaccounted amount of the blasting agent.

They had been lucky that nobody had visited the office and that the lawyer couldn't afford a cleaner. But a little luck should be allowed.

Charlie raised his hand with his wrist in a cast and waved while David and Colby came over. Don signaled his greeting by a wave from the conference room, the telephone firmly pressed against his head. They still had more than enough to do, even now that the immediate danger had passed.

"How are you?" Megan smiled at the professor.

"Good, good. Thank you," Charlie said. A smirk appeared on his face. "I thought I come over and ask you whether you want to teach my freshmen class."

While Megan raised an eyebrow, David voiced their question. "What?"

"I've heard that you came up with a lot of possibilities to use pi."

Snorting, Megan crossed her arms. "You said pi and we jumped. But seriously I'd never looked for the Greek letter in a pattern on a map. How come?"

Charlie shrugged. "It's a fluke. I calculated the probability for the different possible victims by proximity, how long the feud had been going on and so on. The highest probability that hadn't been hit yet, had been a lawyer. His office was exactly where the top line met the second leg of pi and it just fitted."

"So, you didn't calculate anything with pi?"

"No. Hence, the reason your work is so impressive." Charlie gave them a proud smile. "I just wanted to tell you that the locations on a map look like a pi."

"Great," Colby grouched. "I spent hours trying to do math and the solution is a Greek letter." He clapped David on the back.

"So, I guess I can't persuade you to accept an appointment as a visiting professor?" Charlie grinned. "Then I need to give the good news Don — I need somebody to take over my classes until this," he raised his wrist, "is healed and seeing as he knows how I think ..." Charlie trailed off and strolled to the conference room where Don just finished his call.

Megan glanced to the grinning faces of Colby and David. "That won't end well."

"Maybe not for Don," David said.

"Or Charlie," Colby added as they watched Don vehemently shaking his head. "But fun for us."

"Brothers. They know each other so well but don't ever want it pointed out." Megan smiled and returned her focus to her work. And in case of Don and Charlie — they mostly didn't even know just how well they knew each other. But it was time for them to learn it — it was the base of their friendship that surpassed their kinship.

"No way, Chuck! You have to ask Amita!"

Megan smirked. Some things would and should never change.

END

A/N Thank you for reading!