"It's about time we got another chance to show the Foot who's boss," Raphael said, jumping the turnstiles and continuing into the lair.

Michelangelo followed him soon after. "Yeah, son! We crushed 'em!"

Raph and Mikey exchanged a high three.

Leonardo walked up beside them. "They didn't stand a chance! I'm gonna go give Sensei tonight's report." He left for the dojo.

Michelangelo lunged for the video game console and picked a controller off the ground. "Hey Raph! You up for a game of Ultimate Kung-Fu Battle 4?"

Raphael stretched. "Nah, I'm about done for tonight. I'm gonna hit the hay pretty soon."

Mikey turned towards the lair entrance, where Donatello was just crossing. "What about you, Dee?"

Donnie had his gaze focused on a footbot's saw arm which he held in his hand. He snapped out of his thoughts at his name, then took a moment to mentally replay what Mikey had just said. "I'm good. I still have work to do."

Michelangelo redirected his attention to the screen. "Singleplayer, huh? Guess I'm going quest mode."

Donnie left Mikey to his gaming and continued to the lab.

Donatello paused and gave the place a good look upon entering.

His workspace was just as he'd left it, with a half-finished upgrade for the Stealth Bike sitting on his desk. The biological diagrams on the walls were so familiar by now he never noticed them, but would sense it at once if they were missing. The trophy shelf sat proudly over his desk, displaying various strange items.

Pools of algae they had used as a dependable food source sat off to the right, the pools sunk into the ground. He still maintained those in case they should lose access to outside food.

A bookshelf stood in the corner behind his desk, surrounded by various treasured photos of his friends and family.

Everything was so familiar, yet it all felt so different.

Had Raphael not pulled him away from the footbot's saw, which Donatello now held in his hands, he never would have set foot in this familiar place again.

The next time his brothers came in here, it would have been with heavy hearts and tearful eyes. It would have been a reminder of this night gone awfully wrong. It would be a reminder of the one they had lost to an accident in a fight- although, Donatello mentally corrected himself, it wouldn't have been an accident at all.

How desensitized had they become to the fact that people were constantly trying to kill them, that Donnie had mislabelled what would have been his own murder as an accident?

Maybe his brothers would remember this place for something else after the so-called accident. Maybe they would have taken him here and laid him on his own work table to try to stop the bleeding. Maybe they'd have to eventually go back to the lab, not only reminding themselves of him, but of where he had passed.

Donnie shook himself out of these thoughts and crossed the lab to sit down at his desk.

He set the saw aside and resumed his work with the upgrade.

Donatello had given the Stealth Bike some new features similar to the defenses in the Shellraiser, and he was currently working on a control panel for them to attach to the bike's dashboard.

He pulled one of his desk drawers open and searched until he found the tools he'd need for the said project.

Donnie got to work, sorting wires and their respective places on the circuit board. He labelled each wire, or group of wires, that triggered an individual defense mechanism on the Stealth Bike, and labelled where they went before attaching them.

Every time he caught a glimpse of the saw laying on his desk, he'd stop and stare at it.

He'd told his brothers he wanted to keep the circular saw blade because he needed a new one.

He didn't need a new one.

Still, the object commanded his attention.

He tried to get back to work, but found himself staring at it again within only a few minutes.

Donatello decided he wouldn't be able to get any work done with that thing on his desk, so he opened his drawer and grabbed the saw blade.

He stopped, though, before he was able to put it in.

It felt strange to hold it in his hand, when in slightly different circumstances, he would be holding it in the flesh of his neck.

Donatello looked at his own reflection in the metal. Still intact.

For the life of him, Donnie couldn't figure out what it was about this particular weapon that had him so intrigued; he'd had near-misses with countless weapons- Kraang blasters, Foot swords, even occasionally his own brothers' weapons.

So many near misses. So many times something could have gone so horribly wrong.

And yet it hadn't.

The sheer improbability of him surviving all those instances was enough to send a shudder down his spine. Statistically speaking, his next close encounter would be his last, long overdue.

He could say the same about any of his brothers. What if Donnie wasn't paying attention when one of them was about to receive a killing blow?

What if Raph hadn't been checking up on him at that exact moment tonight?

Donnie could say that the last time he'd almost bit the dust. What would happen if he hadn't come out alive last time? Or the time before that? Or the time before that? What would have happened to his brothers if the first time he'd ever had a scrape with death as a child, death had won?

Donatello jumped at a knock on his door.

Splinter stood in the doorway, watching him with a tilted head and perked ears.

"Sensei?"

"I came in here to wish you goodnight and tell you not to stay up too long," Splinter said. "You need rest, my son."

"Hai, Sensei," Donnie said. "Goodnight."

Splinter stroked his chin. "Are you alright?"

Donnie nodded. "Yeah, yeah I'm fine. I just…" He grasped for the words, gesturing nonsensically before settling on knocking on his own skull with a reply of, "Eh. Brain."

Splinter raised a brow. "Surely there is a more detailed way of phrasing it than that?"

"It's just…" Donnie sighed. He hadn't wanted to go into detail when Splinter was only wishing him goodnight, but it seemed his Sensei was welcoming deeper conversation despite the late hour. Donnie tried to organize his thoughts and figure out where to start. "It's just that there's infinite possibilities, infinite outcomes. Every choice someone has made, whether it be a human or a bug, has changed the very course of history. Every choice results in something else, and every big choice sways a lot of different outcomes. There are so many choices, so many events, especially major ones, that have sculpted the path we are now on. But there's an infinite amount of options that could have changed it, and an even larger amount of events that could have occurred instead." He took a breath, having sped up through his entire monologue.

Donnie reined in his pace under control and spoke very clearly. "So why, out of all those possibilities, are we on this specific path?"

Splinter stroked his chin with a thoughtful "Hmm."

"I've done the calculations, and the possibility of the events that transpired the night you adopted us are infinitesimal, even putting your existence, ours, and the Kraangs' as given factors. And if those events hadn't occurred that night, what would have happened to the Kraang? Who would have stopped their invasion?

"Furthermore, each decision and occurrence we experienced as children led to us learning something new and reacting and growing accordingly, which is why no two people turn out the same, having a unique set of childhood experiences that determine the shape of the lessons they learn, and therefore, their personality as they grow. How would our takedown of the Kraang plot have been affected if one of those experiences was slightly different?"

Donatello paused to give Splinter time to respond, but Splinter seemed content to let Donnie talk and let the thoughts stew.

"There's so many things that could have been different, things that could have changed if something was just a little different, but there's…"

Donatello trailed off.

"My son?" Splinter asked when Donatello did not start talking again.

Donnie scratched his neck. "There's, uh, one variable that throws everything we've done- all the impact we've had on the world- there's one variable that could have changed all that, and it's… can I… can I ask you a question?"

"Of course," Splinter replied.

"When you went to the pet store," said Donnie, "Why did you go in with the intention of buying four of us?"

Splinter blinked. "What do you mean?"

"Psychological studies show that people find certain numbers more appealing. Now, to get one pet would be understandable; that's the most common number, when getting a pet. People think they might get overwhelmed if they have to make the sudden transition from caring for no pets to two pets. For turtles, I'd say two would also be a common number to buy, seeing as some species of turtles are social, but not particularly to humans, so they need other turtle companions to keep them happy and healthy. Three is also a common number to choose, as it is one of those psychologically appealing numbers, and people just generally have a tendency to lean towards three.

"But after that, the next number people tend to go for is five. Five, being odd, is more appealing than four. People don't really find four an appealing number, and they usually don't tend to choose four, given the option. Four is an odd number." He shrugged. "Statistically speaking, of course. Numerically speaking, it's even, obviously.

"Five also might have been too many turtles for a man living in a crowded New York City apartment, so it seems like the choice you should have gone with is three."

Donatello tried to stop himself there. He was rambling, and he knew that if he opened his mouth again, he was liable to go on another tangent. Splinter still hadn't answered his question, and Donnie wanted it answered before it got lost in the social standard of being mentioned too long ago to be relevant to address.

But Splinter still didn't talk, and Donnie tensed, wondering if he'd caught Splinter off-guard with his ramblings. Maybe Splinter had planned on going to bed soon and Donatello had thrown his plans out the window?

Splinter was still thinking it over, Donatello tried to tell himself. Splinter had urged him to discuss what was on his mind, and his anxiety was just telling Donnie that he was being a nuisance.

Then Donnie remembered once when Splinter advised him that if he wanted information, sometimes the best tactic was to remain quiet.

Donatello found that it was a tactic that worked on Mikey plenty of times when the youngest insisted that he hadn't done what he wasn't supposed to. Michelangelo was always one to fill in awkward silences with talking, which came in handy when the team needed to form allyships with people they weren't familiar with, but when Michelangelo knew he'd done something wrong, it was only a matter of time before he gave away a detail that didn't line up with his story.

Donnie mused Splinter could be using the same strategy on him right now, not to get him to slip up and tell Splinter something he'd done wrong, but to lure Donatello into sharing his thoughts more in-depth.

Donnie decided to push on, hoping this was the case.

"But if the number it seems you should have chosen was three," he continued, "It raises the question, how have things changed because you chose four? How would they have grown and developed, what impact would they have had on the world, if… if I wasn't here? Would they have kept the Kraang and Foot at bay all the same? Would they have… would they have defeated them for good already?"

Splinter tilted his head. "What makes you so certain that you would have been the one left behind?"

"I-" Donatello blanked. When had he made that conclusion? He retraced his thoughts, but couldn't find any stream of evidence or logical thought he'd followed to come to that verdict.

All the same, it felt like the right one. When he thought of any of his brothers not being there, not being themselves, it just felt wrong.

"Isn't it obvious?" He asked, despite not quite knowing where he was going with this. It was just the right path in his mind, logically explained or not.

"It is not," Splinter said.

Donnie stood and walked over to the lab door, gazing out at the living area where his brothers usually hung out. "The guys, they… they work like clockwork. They complete each other. You couldn't imagine one without the others."

"And you believe you are different?"

"Well, yeah. I'm not part of their… rhythm. I'm up here in the lab so much of the time, and they're all down there, interacting with each other and learning how to work together. Even as a child, before I was knee-deep in inventions, I was always off to the side, doing my own thing. I wasn't really involved with them, and I'm still not, and…" they probably wouldn't even notice if I was gone, his brain supplied, but he decided not to say such out loud. He was already dumping too much on Splinter as it was.

"Do you ever listen to concert band music?" Splinter asked.

Donnie blinked. "Sorry, what?"

"Or maybe orchestra," Splinter suggested.

Donnie's brow furrowed. "Uh… yeah, I guess. It's in the background of movies all the time, so I guess I wouldn't say I listen-listen to it, but I'm familiar."

"So you hear how the instruments sing as one," Splinter said. "How the flute and the saxophone and the tuba all have different voices, different qualities, and yet they come together to create a beautiful tune."

"Um… yeah?"

"This is what you see in your brothers?"

Donnie scratched his head. "I mean, that's a strange way to put it, but yeah."

"But there is an instrument that does not sing," Splinter continued. "It is not there to build the melody or harmony; it only sounds intermittently."

Donatello followed his thought. "The drums."

Splinter nodded. "The drums do not sing with the rest of the orchestra, and perhaps they only join in the music every few beats, but that is their purpose. They do what the other instruments were not designed to: keep the pulse. Drums are the most rhythmic, perhaps most analytical part. But a drummer's technical knowledge, of tempo, of rhythm, keeps the rest of the music in line so that it can sing without losing control."

Donnie clasped his hands together under his chin.

"Perhaps you were meant to be more independent, my son," Splinter said, "But that does not mean you are not part of your brothers' rhythm. Your skill set might not be as socially inclined, but time and again, it has saved your brothers' lives. It has kept their pulses."

"Maybe." Donnie nodded. "Maybe." His expression soured. "But if I am just as much a part of them as they are of each other, then that makes the prospect of only three of us existing all the more… frightening." He glanced at the sawblade on his desk. "The statistics of it all are petrifyingly low." He walked over to the desk and picked the blade off of it, then mimed the path the footbot had taken earlier to plunge the saw next to his neck. "One thing gone wrong, and the Kraang might have taken the world over already without us to stop them. How much longer until…?" He looked over his shoulder at Splinter. "How long until statistics win? And after we're gone, will there be anyone to stop the Kraang before…?" He shook his head. "Some things are just out of our control."

"Interesting thoughts indeed." He walked closer to Donatello. "You asked earlier how I decided to adopt all four of you?"

Donatello turned around, lowering the saw blade. "Yeah. Why did you walk into the store with the intention of buying four of us?"

Splinter smiled. "I didn't."

Donatello tilted his head.

"You see, I originally walked into that pet store with the intention of adopting a dog."

Donnie blinked. "Wha-"

Splinter chuckled. "Yes. Like you said, I lived in a cramped New York City apartment, and I was going everywhere to search for a dog small enough for it to consider my apartment spacious. You see, my wife and I had a dog before Miwa came along, and every day when one of us came home, he'd race to the front door, barking and carrying on like he hadn't seen us in years. It was often the best part of the day." He smiled at the memory. "So when I moved to New York, I quickly became lonely without my family. I remembered the joy this small dog had brought me and decided to search for a new one.

"I went from store to store trying to find a new dog, but something did not let me settle on any of the ones I saw. I had thought, at the time, it was due to none of the dogs being my previous one. I would later find it was intuition.

"At first, I had overlooked the pet store where you four were, but the same intuitive feeling eventually drew me there. I looked at the store's dogs and became confused when my intuition did not point any of them out to me.

"But then, I saw you boys in the turtle tank, and my intuition led me to all of you.

"At first, I tried to talk myself out of letting my intuitive sense control me- turtle tanks are large, and I had no space to put a tank large enough for a turtle to have a free space to swim, let alone a tank large enough for two, as like you said, turtles are social creatures and are healthiest to be adopted in pairs.

"But I could not leave. I told myself to leave the store and go onto the next in my search for the right dog, but my training in self-discipline failed me. I simply could not leave.

"Eventually, an employee approached me and asked me if I wanted to adopt. I figured I would do so and figure out space arrangements later, when I got back to the apartment." He chuckled. "Which, you know how the story goes. Apparently fate had different ideas."

Donnie nodded.

"The employee asked me how many turtles I wanted, to which I responded four, without thinking over the answer. I panicked a moment later, realizing I would have to get a big tank once you boys had grown, but something told me not to change my response. It fit, somehow. And so I went into the shop with the intention of getting a dog and walked out with four baby turtles, and you know the rest."

"Your intuition," Donnie said. "Your intuition is what made you get four of us."

"Yes."

Donnie drummed his fingers on the desk behind him and stared off to the room's corner. "Do you ever…" he sighed. "Do you ever think about if it was the right choice?"

"If you are suggesting I would rather have three sons, then banish the thought from your mind. I am ever grateful that my intuition drove me to adopt all four of you." He put his hand on Donatello's shoulder and made sure his words sunk in.

Donnie nodded.

"As for the possibility of adopting more- I have sometimes considered what it would be like to have another child in the family. However, I do believe that what I felt was meant to be in that moment, still is. You are right. Out of all the possibilities, all the realities that we could be facing right now, this is the one that has come to pass. And you and your brothers, having as great a bearing on this reality as you do, your past and present all depend on that choice I made fifteen years ago. But here we are, on a path where the Kraang and Foot have not taken over, thanks to you and your brothers." He closed his eyes and nodded. "Despite all odds, all the statistics you have run of what could have been, here we are."

Donnie stared down at his hands, as if he was seeing them for the first time. He raised one to his neck and ran a finger over the line where the saw blade had nearly hit.

His mind raced a million miles a minute, but refused to work all at once. There were a thousand questions to be asked, and he had to struggle a few moments to find the words to form just one of them.

"So you're saying out of all the potential realities, this is the one we're on because the choices that lead to better realities are more appealing?"

Splinter hummed. "I suppose you could say that." He stroked his beard. "Intuition is a very mysterious thing."

"I wonder if intuition is something that can be explained psychologically," Donnie thought aloud. "I mean, people have strange feelings based off about what's going to happen or what to or not to trust that they can't explain up-front, but it's actually based off of details they've picked up subconsciously, but haven't consciously processed- like how people know who the plot twist villain will be in a movie even before it's revealed. The viewer might not consciously pick up details that condemn the villain, but their subconscious brain analyzes patterns and sends an alarm when things don't add up."

"Perhaps," Splinter said.

"But if people really can sense the choices that will alter reality, then is the path we're on based purely off of how well-developed people's intuitive senses have been in the past?"

"Of course," Splinter said. "They might not have known that their choices were so life-altering, but as you said, each choice creates a larger effect. And intuitive choices are sometimes a lot simpler than the word might make them appear. Sometimes, the choice is as simple as whether or not to… say, rob a bank."

"Well, that doesn't sound like a good idea at all!"

"No, it does not. Because when the choice is presented to you, you can foresee that possible reality going wrong for all involved, can you not?"

Donnie nodded.

"See? Your intuition helped you to shape a better reality."

Donatello's eyes grew wide. "It's just choices?"

"Just choices. All the same, those choices have gotten us here. The statistics may say that this reality is improbable, but through people's intuitive senses, we have stayed on a path where you and your brothers are all alive and well and ready to defend the city from its various threats."

"The statistics are flawed," Donnie realized aloud.

"I hope this does not discourage you?"

Donatello chuckled. "No. Statistically speaking, we'd all be long dead by now. It's… kind of odd, thinking that the most scientific of approaches can't calculate everything, but hey. If four is an odd number, statistically speaking, then why shouldn't intuition be able to steer our reality? It's… it's actually kind of comforting."

"I am glad," said Splinter with a warm smile.

Donnie returned the expression.

Splinter seemed to consider something, then his smile faded. "You implied earlier that you were feeling disconnected from your brothers."

Donnie shrugged. "Yeah, it gets to me sometimes that I'm not as involved with them as maybe I should be. Even if I am doing what I can to help them in the lab."

"Your scientific work has served the team well time and again," Splinter said, "But if you feel this way, then perhaps you should follow your intuitive sense and act on the problem."

Donatello gave a halfhearted chuckle. "I see what you did there." He hummed. "But if the analogy is I come in every once in a while as the drum to their band, then maybe I should add cymbals?"

Splinter laughed. "This analogy has become a little convoluted, but yes. Add cymbals."

Donnie looked out into the living area, where Mikey was still questing away at his video game.

Donatello gave Splinter a meaningful smile. "Thanks, Sensei." He hugged his father.

Splinter warmly returned the gesture.

Donnie pulled away and walked into the living area. "You still up for a multiplayer game?"

Michelangelo sat up with an ear-to-ear grin. "Yeah, bro! Grab a controller and jump in!" He tossed Donnie a controller. "Done with your science-y stuff early tonight?"

Donatello turned the controller on. "Nah, I didn't really get much done tonight. I just had a conversation with Splinter about existentialism, but you know what? I really just needed to add cymbals." He relished in his baby brother's bewildered expression.

Mikey gave him a thumbs-up and a halfhearted "Yayyyy", obviously unsure of whether such was the correct response, then quieter, "I have no idea what you just said."