"Man, we really need to clean this place out one day."

Bemused, Myungsoo looked up from the file he was reading and at Daehyun, who was staring at a bulging box of folders with an expression close to despair. "Remind me again why you have a computerized database and  a hardcopy one? Isn't that just more work for you and the janitors? I mean, imagine the amount of trees you could save if you got rid of that system."

The Yangsan agent grimaced and poked the box. Once he decided it wasn't going to spit dusty papers at him or anything of the sort, he began to pull at the folder crammed into the far end. "That's what a lot of people here think, too. We'd save a ton of ink and paper, not to mention nobody even uses this room, anyways. At least, nobody that I know of."

Pausing in his speech, Daehyun focused on the task at hand. He gave the stubborn folder a hard, forceful tug, then grunted as it came flying out of the box.

Pleased with his success, he continued. "But I get why this hardcopy database was made. In case anything happens to our computer files- a virus, a lockdown, or even a technical issue, like what happened today- we have these paper copies as backup. Why do you think I wasn't as worried when the intelligence guys told us we couldn't use the data room this morning? Everything we need is right here, crammed somewhere in a musty corner with 40,000 other papers. So really, this room isn't a waste of space... even if a forest was killed in the making of these files."

Myungsoo merely shook his head and resumed his work. It was his third and final day in Yangsan, and he was currently in the station's main filing room with Daehyun. It was just the two of them for the moment- Ailee was in a meeting with the branch director, and had promised to join them later at noon. In the meantime, the two men were looking for records of past cases, hoping they could provide an answer to a certain skeptical, but possibly credible theory.

"What puzzles me the most," Ailee said, frowning down at her notebook, "Is the common factor linking together the victims. Or rather, the  lack of a common factor." She glanced at the other two agents sitting across from her.

"An elder. A family man. A university student. A retired widow. And a CSI agent, though that's yet to be confirmed. What do these people have in common with each other that's bad enough to justify their deaths?"

Daehyun crossed his arms in a thoughtful manner. "Maybe they're all distantly related and the Mockingbird is killing them because of a family feud. Or maybe they're part of a witness protection program, and this is his way of getting revenge. What do you think? Want me to get these theories checked by intelligence?"

"No need," Myungsoo replied. "We already thought of that back in Seoul. None of these people are related to each other, nor are they part of a protection program." He eyed his own case notebook, which was laid out on the table in front of him. The heavy writing looked like a mess of inky scribbles and lines, giving him a headache just by simply looking at it.

Ailee pursed her lips. "It's as if the victims were picked randomly out of a hat... No, not completely. There  is one thing that connects them together, now that I think about it. It's very farfetched, but it's all I can think of at the moment."

"And that thing is..." Daehyun prompted her.

"Science," was his partner's cryptic reply.

Daehyun furrowed his brows. "Science?"

"She's right," Myungsoo agreed. He recognized where Ailee's idea was going. In fact, he'd first heard it from Kris, back when he was still on the case and the agents were collaborating together in a meeting. "Science. Or rather, the scientific field of study and all things relatable."

Seeing Daehyun's still-confused look, Ailee proceeded to explain the new theory. "It's simple if you think about it. If you examine the victims' profiles carefully, there's one main factor that links them- well, the majority of them- together. Where did the elderly Lee Seonwoong work in his past? At a biomolecular research firm. What about Son Taehyun? At an apothecary shop. And Kim Hwayoung?"

"In a retirement home," realized Daehyun, thoughts running a mile a minute. "But we interviewed her son over the phone yesterday. He told us that before she worked there, she was with a pharmaceutical lab."

"That's right. A pharmaceutical lab."

The Busan man exhaled. "But that doesn't explain Lee Minhee's case. Why is she involved? She was just a student majoring in interior design."

"I know." Ailee's frustrated expression matched that of her partner's. "That's what confuses me." And judging by the tone of her voice, being confused was the last thing she liked to be.

"We looked at her family's register," Myungsoo offered as a way of explanation. He flipped through his notes, trying to ignore the heavy scribbles boring into his eyes. "Let me see... Her parents worked at The Institution for Higher Living, which is located on the outskirts of Seoul. A medical laboratory. They died from gas leak in the building twenty years ago, along with six other workers. After their deaths, Minhee was sent to live with an aunt, unil she became old enough to look after herself."

"The Institution for Higher Living, huh..." Ailee mused. Her eyes lit up. "Then it might not have been the child the killer was after. Maybe he targeted her because of her parents."

Daehyun winced. "You think so? It seems like a shallow reason to me. How could somebody kill a young girl just because of her parentage?" 

"People have killed for less," his partner reminded him grimly. "At any rate, I think we could be onto something. Until we find something to disprove it, we should follow this lead and see where it takes us."

"Are you sure?" Daehyun still seemed skeptical.

Ailee gave him a firm nod. "As sure as I'll ever be. Don't give me that look, Daehyun. It might not be a strong enough theory to you, but it's all we have right now. So let's get to work."

And that was how Myungsoo and Daehyun found themselves in their current situation. In light of the proposition that science was the link between the victims, the pair was searching for previous cases which related to that specific subject. Ailee was firm in her belief that the Mockingbird had chosen his targets because of it. Perhaps she was right. There was a chance that he, along with his victims, had been involved in a past case relating to the scientific field... But until they found the evidence, they would have no way of making sure.

Daehyun grumbled. "Of all the days to get a malfunction, the computers chose today. Look at all of these boxes and filing cabinets! It'll take us at least a week to get through them all."

"Didn't they say they'd fix the system by this afternoon?" Myungsoo asked, not looking up from his papers. "We just need to get started here, and search up what's left on the database."

"Well, yes," Daehyun admitted, "But either way, there are too many files to look through in here. I can't remember if I mentioned this before, but these aren't just records of Yangsan's cases. There are files from the National CSI Database, as well. We have records of all the investigations that took place in this country."

The Seoul agent blinked at him, then glanced at the shelves around him. "Really? You have all  of Korea's crime scene reports in here?" While the room was jam-packed with folders, he highly doubted it contained every single file from the nation's database.

"Not all of the records are in here specifically." Daehyun put his folder down and began rifling through the rest of the box's contents. "Most of the older ones are in the basement. We try to keep the ones in this room fairly up-to-date."

"Hmm. At least you have a thorough system," commented Myungsoo.

Daehyun rolled his eyes. "It's a bit too  thorough, in my opinion. But yeah, I guess you're right. At least we won't have to worry about losing important data on our computers." 

A comfortable silence fell upon the two agents. It went on like that for the next half hour: both men thumbed through piles of folders, occasionally pulling out the ones which caught their eyes. Once in a while, Daehyun would make a comment about an interesting case he had found, and Myungsoo would murmur quietly in response. Although the task was menial, it helped distract the dark-haired man from thoughts that had been bothering him since his departure from Seoul. Thoughts of Yongguk. Thoughts of Sungjong. But most troublesome of all, thoughts of a missing newcomer...

Twin pools of intense brown stared back at him, reflecting none of what the owner of these guarded eyes was thinking inside-

"- Myungsoo? Hey, Myungsoo? Are you listening to me?"

The sound of Daehyun's voice brought the agent back to reality. He forced his mind to focus on what his companion was telling him. "Sorry, could you say that again? I was... thinking about something else."

Daehyun gave him a curious look, but repeated his words either way. "I said, I just remembered something I read about this investigation a few days ago. Case 21, I think it was called. Some of your people found a whole bunch of lab notes in one of the victims' houses, right? Do you think that has something to do with the case? I mean, if we go with the science theory, there's a very high chance that that's the link we're looking for."

"We don't know yet," Myungsoo responded. "Woohyun and Chanyeol, the guys who found the notes, are working on it. But last I heard, they haven't managed to decipher any of it yet. It's a lot more complicated than it seems. Whatever Lee Seonwoong intended to do with his research, he kept it a very well-guarded secret from the world."

"I see." Daehyun pushed aside a box and pulled apart the flaps of another one. "Well, I hope they solve that puzzle soon. I don't know why, but I have a feeling this Case 21 could be the key to uncovering the mystery of the Mockingbird."

----------

Later that evening, Myungsoo found himself sitting alone in his car. It was only 7 PM, but following traditional late-November weather, the sun had long set and left behind a world of darkness. The man glanced at the steaming cup of coffee he'd purchased for the drive back to Seoul. He supposed he could have stayed in his hotel room for another night. The nightly rate wasn't that expensive, and if he did, he could have finished some more work in the Yangsan station. But truth be told, Myungsoo didn't want to. The drive wasn't long, only three hours if traffic was good... But more than that, it was because he just didn't want to stay in Yangsan. He didn't quite feel comfortable here. Yes, it was his hometown, but it held so many strange and detached memories of his past... Of his parents. Plus, not having Sungjong around made the town seem all the more unfamiliar to him.

Sungjong. The kiss. In the cemetery. He kissed me. My best friend. Sungjong.

Myungsoo shook his head. Reaching for his coffee, he took a long gulp before placing it back on its holder. He trailed his eyes towards the clock on the dashboard. 7:03, it read in little red lights. His colleagues back at HQ would have left work an hour ago, he realized. After debating with himself for a moment, he pulled out his phone and scrolled through the contact's list. A quick call before setting out on his drive wouldn't hurt.

Brring, brring... Brring, brring... Myungsoo frowned as the phone's dialling tone droned on. Why wasn't anybody answering? It wasn't work time, not was it close to bed time. Unless the person he was calling was out drinking, he almost always answered his incoming calls.

Just as the raven-haired man was about the end the call, a man hurriedly picked up the receiving end. "Hey! Sorry, I was answering the door. Some lady lost her dog and wanted to know if I saw it. Anyways, what's up, Myunggie? It's been forever since we last talked."

"Don't call me that." Myungsoo automatically cringed at the nickname. "And hi, Woohyun. Don't be so dramatic. It hasn't been that long. Only three days since I left Seoul."

"Well, it's been three days too long without my dear friend," the older inspector answered in a cheesy voice.

Myungsoo rolled his eyes, but then remembered Woohyun couldn't see him over the phone. "Save the grease for Sunggyu, pal. I have a three hour drive ahead of me and I plan on getting home in one piece."

"So you're coming home tonight?" Woohyun hummed. "Good. I was getting bored at work without having your ugly face to entertain me."

"Why am I even friends with you?" Myungsoo snorted, but nonetheless, he felt a smile tug the corners of his lips. "Anyways, listen, I wanted to get an update from you before heading back. Did you find anything new about Case 21?"

Woohyun released a breath. "Nope," he said. His cheerful tone turned into one of frustration, which told Myungsoo that deciphering Lee Seonwoong's notes were indeed proving to be more difficult than expected. "I've spent all week trying to decode the old man's papers, but all I've found so far are a coffee stain and a list of groceries he threw in there. I'm telling you, the equations are killing my head. Chanyeol hasn't had much luck, either."

"Have you tried asking Youngjae?" Myungsoo wanted to know. If there was anyone who would have a clue as to what the notes were about, it was Youngjae. There was a very high chance that the intelligence agent could help Woohyun make some sense of what was in Seonwoong's notes.

"I haven't had the chance yet," his friend answered. "He's too busy trying to track down that black market trader. And I tried asking some other guys from intelligence, but they were lost, too. In the meantime, I've been trying to set up appointments with a few biomolecular and chemistry university professors to see if they can help. With any luck, I'll be able to meet them within the next two days."

"Everyone's so involved with this case," mused the younger man. "I can't remember when the last time was we were so serious."

"Yeah." Woohyun gave a short bark of laughter. "Too bad we haven't seen any results yet."

"We will. Soon," Myungsoo said, although even to his own ears he sounded completely unconvinced of his words.

Woohyun laughed again. "Sure. We can at least hope, right? Anyways, moving on. We haven't discovered much of anything else. Hoya still hasn't gotten any answers from Kim Jongin. All that guy does is sit in his cell and stare into space. Sometimes he cries and mumbles to himself, but nobody's managed to get a response from him. Still no solid suspects, although Chen and Sungjong are trying hard with their interrogations. Oh, but you'll like this- Kris is leaving the hospital soon. Well, he was supposed to stay for another week, but they bumped it up to tomorrow morning."

"Already?" Myungsoo was surprised. He also felt a twinge of guilt at the mention of the sandy-blonde agent. He'd been so caught up with the investigation, he hadn't found the time to visit or even call to see how the giant was doing. "Didn't the bullet shatter his bone, though? I thought he would have had to say for longer."

"It didn't completely shatter the bone. Only a small fraction of the tibia," Woohyun corrected. "But it hasn't fully healed, either. He managed to convince the doctors to let him out early. I personally think he threatened them, but apparently his argument was that he couldn't stand watching from the sidelines and not being able to do anything." 

"That sounds like Kris alright. Good to know the bullet didn't kill his stubborn streak. But there's no way Sunggyu will send him out on the case." An image of Kris hobbling on crutches after a masked man came to Myungsoo's mind. "The boss would sooner send him back to the hospital than out to do field work."

Woohyun snickered. Judging by the degree of amusement in his voice, he was most likely imagining the same thing as his friend. "Too right, buddy. But good ol' Kris said that it's his head, not his legs that he needs to investigate murders. He's willing to work within HQ. I guess after being stuck in bed with nothing to do, it'll be good for him... Plus, this is strictly between you and me, but I kind of miss having that guy terrorize the station."

Myungsoo chuckled. "You and me both, pal." And probably everyone else in the building, too.

They then fell silent, the two Seoul agents. Myungsoo traced the outline of the steering wheel with his free hand, unsure of how to continue the conversation. Woohyun was probably distracted by something on his laptop, which was why the normally chatty man wasn't talking. Either that, or he was lost in deep thought about the crazy events that had happened over the past three weeks.

Finally, after a long, drawn-out moment of fiddling with the wheel, Myungsoo took a deep breath. "So... What about Yongguk?" He swallowed hard as the face of the deceased artillery expert flashed in his head. "Anything on him?"

Woohyun cleared his throat. "No. Nothing besides the autopsy report. Dongwoo let us know just today, actually. He said that Yongguk did die on the night before Amber discovered him. It wasn't a copycat murder, but the bird was placed on his stomach. Approximate time, 2:45 AM. He... He was chloroformed first, then shot once in the chest with a G3A3.20 rifle. The same one used on Kim Hwayoung." His voice dropped down a notch. "Chaerin confirmed it."

"... How is she handling it? And Amber, and Zelo, too?" Myungsoo gazed at the clock. 7:20. The red numbers seemed to warn him that time was ticking, that he'd better hurry back home already and prepare for the next day. But as childish as it was, a part of him wanted to run away. He didn't want to return to the sorrow that was waiting for him there. He was getting so sick of it. Sick, tired, and ready to get away from the pain that was wearing him down.

He averted his eyes away from the clock. "I mean, I know everyone's upset about Yongguk, but those three were the closest to him. Especially Chaerin and Zelo. I rarely ever saw them without each other."

"I know what you mean," Woohyun answered solemnly. "Chaerin's coping well. Obviously she's really torn up about it, but she doesn't let it show as much. Gotta admire her strength. Amber's doing okay, but I'm using the word 'okay' very loosely. Since she was the one who found the body, the shock affected her greater than it did with others. She's starting to pull out of it, though. But Zelo..." He hesitated.

"I've never seen Zelo look so down before. No, saying that he's down is a total understatement. It's like he's in a deep state of depression, and nothing can snap him out of it. He still comes to work, but acts like a zombie most of the time. But this morning, Sunggyu tried giving him a couple of days off to recover. The kid refused. Said he couldn't just kick back at home while the man who killed his commander was roaming the city. He even asked to join the investigation, believe it or not. Sunggyu decided not to argue and put him with Hoya for now. I think it was a good choice. It's put some life back into the kid, for starters."

Zelo's condition wasn't news to Myungsoo. Out of everyone in HQ, Yongguk had been the closest to the junior weaponry agent. Anybody in the station could tell you that they were more than just senior-junior colleagues. The two were close friends, practically brothers, a master and his young protégée. Although the agent was still saddened by the loss of his friend, he knew his pain was nothing compared to that of Zelo's.

There was another silence. A thousand different thoughts were running in Myungsoo's head, each moving along on their own winding path. Sungjong, Yongguk, Zelo, the Mockingbird... And...

Perhaps Woohyun sensed what his friend was thinking about, because the next thing he said was:

"It's not looking good for him."

"What?" Myungsoo was started. "Him... You mean Sungyeol?" Something tugged at his chest. He had gotten used to visualizing the newcomer in his head, only thinking about him wordlessly, that hearing his name fall from Woohyun's lips was like having a pair of defibrillators jump-start his heart. Not a good sign.

His friend's voice took on a grim note. "He's been missing for four days now. People are starting to think it's because he's gone in hiding. You know, because he's the killer and he knows we're on to him."

Myungsoo gaped into his phone. "That's ridiculous. Why would he go into hiding? It's not like he's the killer..."

A voice tutted in the back of his head. You ignorant fool. How many times have we gone over this? We don't know whether he's the Mockingbird or not. Where's the proof that he's innocent? Nowhere, unless he decides to show his face again. And even if he turns up, he'll be seen as a suspect more so than a victim.

The older male exhaled loudly. "I don't think he is, either. But things are starting to pile against him, Myungsoo. He's been reported as a missing person, but the police aren't doing anything about it because they think he left home willingly. Like, he wasn't kidnapped and stuff. The only proof we can give to claim him as missing is the fact that he's not showing up for work. And even that isn't enough to start a search." He signed again.

"If Sungyeol ever comes back-"

"When,"  Myungsoo found himself correcting, "You mean when  he comes back."

"Right." There was a pause. "When  he comes back, he's gonna have a hell lot of explaining to do. Besides you and me, there aren't too many people who are in favour of him. I think Sunggyu is, but even he might not be able to throw the light off of him."

The younger man tried to argue back. "Yeah, but it's not like they have solid evidence against him. The fact that he's disappeared doesn't account for anything-"

"Don't forget, he may also be acquainted with that black market dealer, Park Kyung," Woohyun interjected. "But you're right. There's no solid evidence. Though Chen suggested that we search his apartment for clues- ! It's almost 7:30. I was supposed to meet Chanyeol ten minutes ago. Listen, Myungsoo, I have to go now. We're all having a meeting tomorrow at noon, so make sure you're there on time. The usual room eleven. I'll see you later."

And with that, Woohyun bid him a hasty farewell and disconnected the call.

Myungsoo slowly lowered his phone and placed it on the passenger's seat. He stared at the cafe cup in his drink holder, which was still filled more than halfway with the bitter drink. But he wasn't considering taking a sip from it. Instead, his thoughts were running elsewhere, giving him a pounding migraine from trying to make sense of it all-

It was then that the voice spoke up again, like a cruel, merciless memory coming back to haunt him from the past.

Poor, foolish Myungsoo, blinded by the feelings in his heart. Perhaps this will teach you to open your eyes to the world, hmm? Gone for four days, not telling anyone where he is or why he left. For all we know, he could be in Europe by now, hoping to evade Korea's legal system and hide his sins as a killer...

Myungsoo dug his nails into the flesh of his palms. "He's not,"  the agent said loudly, trying to block out the sound of the malicious voice. "He's not in Europe. He's not in hiding. There's no reason for him to be. And besides, where's the proof? All of the suspicions on him are based on assumptions. Think what you want, but Lee Sungyeol isn't the killer. I know he isn't."

But even as he sat there in the dark, all alone in his silent car, he couldn't brush away the seeds of doubt which the voice had slyly planted inside his head.

Lee Sungyeol wasn't the Mockingbird... Was he?

[A/N] There was a major mistake in this chapter, which I'll explain in the next update (which I predict will be in an hour! :))