Disclaimer: The TMNT belong to their rightful owners, not me. I wrote this story with the solely purpose of fun and it is heavily based on the scenes shown in the teaser trailer and the "Behind the scenes" video of the upcoming Rise of the TMNT.

The bet.

Chapter 1. Strangers in the sewers. (Part I)

"Who are these dudes? And what are they doing?" the youngest of the four siblings, Michelangelo, softly whispered.

"Don't know who they are, but they seem to be taking those junks of metal to somewhere," his brother, Leonardo, answered in a low voice.

The brothers had been wandering around the sewers, playing tag and other games, when they had spotted movement ahead of them. Since they were quite far from where the action was taking place, the siblings could only distinguish several human-looking figures running at the same direction. That itself was an interesting event. It was rare to find a person in the sewers, let alone to find an army of funny-looking people. So, naturally, the curious turtles had approached in order to get a better idea of what was happening there.

Now, hidden behind huge stone pillars that were part of the subway infrastructure, the four turtles were watching the bunch of moving figures who were near the entrance of an abandoned tunnel. The ones who went inside the tunnel were carrying large pieces of metal, while the ones who came out from it were empty-handed and, as soon as they looked around to make sure the coast was clear, began running away in all directions.

"Whatever they're doing, it doesn't seem like it's something good," Donatello stated, narrowing his eyes.

"I was thinking the same thing, bro," the oldest of the four, Raphael, said. He turned around to see his brothers and smirked. "I say we should get there and find out what's going on with those clowns. They probably need us to bust their heads," he concluded, cracking his fingers.

His younger brothers exchanged glances while a grin slowly made its way to their lips.

"It sounds like fun," Michelangelo said, his eyes lightening up. "I'm definitely in!"

"I'm in, too," the purple-clad turtle declared, arching an eyebrow and smiling. "I'm intrigued about what they're planning to do with all of those pieces."

Both of them quickly joined Raphael's side and then turned around to see their blue-clad sibling, who was tapping his chin in a thoughtful way.

"Alright," Leonardo said with a shrug. "Since there's nothing more interesting to do right now, then I'm in too".

Raphael and Donatello rolled their eyes at that statement while Michelangelo covered his mouth, trying to supress a giggle. They all knew Leonardo was as much interested in participating on the mission as they were, but he was playing it cool by saying that line just for the sake of teasing them.

"Then, mister 'Nothing-more-interesting-to-do-right-now', bring your shell over here or you'll get left behind," Raphael teased his brother before turning around and beginning to move towards the suspicious figures, followed by Michelangelo and Donatello.

"Get left behind?" With a swift movement, Leonardo joined his brothers and looked at Raphael with a smug smile plastered on his face. "Oh, so does this mean we're switching roles, big brother? Then I'll try to be the slowest one, but you'll have to try your best to be faster than your usual self."

Raphael frowned and gave his younger brother a playful punch in the shoulder. Leonardo chuckled and held his hands up.

"Okay, okay, just kidding, you know?", the blue-clad turtle said, grinning. "Anyway, what's the plan, Raph?"

"First, we'll get inside the tunnel to see where they are taking that junk to and what they're doing with it. Then, we'll punch them really hard," Raphael answered, making a fist with his hand to emphasize that idea. "Or viceversa. Whichever works best."

This time Leonardo was the one who rolled his eyes and smiled. Of course there were plenty of plans that were way better than the ones his brother had just said, but he opted to keep silent. Things tended to be more interesting if there were unpredictable variables in the mix, didn't they? Plus, even though he did enjoy giving his older brother a hard time, it didn't necessarily mean he had to annoy him every single second of the day. After all, he had to be considerate with his two other brothers. They deserved the chance to annoy their oldest sibling too.

And so, the four turtles continued moving towards the suspicious people, always keeping in the shadows and hiding behind the boulders and pillars that were in the place.

When they were a few feet from the entrance of the tunnel, the red-clad turtle made a motion with his hand to signal them to stop. Since the place was quite dark, they could only see the general stuff, like the people's movements and what they were carrying, but specific things? They couldn't. Luckily for them, they had a genius brother on their side. A brother who was always full of useful techy stuff that he built with his own hands and who was now confidently smiling because he knew it was time for him to do his work.

Donatello put his goggles on and began evaluating their possible opponents. Thanks to the night vision feature of his techno-goggles, he found some familiar marks on the metal pieces that those people were holding. However, something else caught his attention…

Was it just his imagination, or were they wearing the typical clothes of a…?

"What do you see, Donnie? Should we send them directly to Painland or not?" the oldest turtle asked in a low voice, obviously not wanting to be heard by the figures and interrupting Donatello's train of thought.

"Mmm… I think we probably should," the genius replied absent-mindedly, moving some buttons that were on one of the sides of his goggles. "But… there's something really odd about these people…"

His brothers looked at him with questioning eyes and waited for the explanation they were sure Donatello was going to give them. The purple-clad turtle fiddled a little bit more with his goggles before he took them off and met his siblings' gazes.

"First of all, do you remember last week's news report about some factories that had been robbed?" The intelligent turtle asked and his brothers nodded, paying all of their attention to his words. "Well, I'm ninety nine percent sure that we've found the culprits. These people are carrying several metal pieces with the trademarks of said factories painted on them…"

"Great! Then let's…!"

"However," Donatello continued, as if he hadn't been interrupted by Raphael, "those people are —how should I put it?— definitely not normal."

"Not normal? So I guess four mutant turtles talking about normalcy is something completely normal, right?" Leonardo mumbled in a barely audible voice and Donatello ignored his comment too.

"But why do you say they are not normal, Donnie?" Michelangelo asked with curiosity, popping his head behind his purple-clad brother's shoulder and squinting his eyes in order to have a better look at the figures. "Do they have an extra head or something?"

Donatello arched an eyeridge and was tempted to give an answer to his sibling's questions, but… Nah, he'd rather not. Instead, he reached for his youngest brother with his arm, placed him at his side and put his own goggles on his sibling's eyes. His brother gasped in surprise and Donatello couldn't help but half-smile.

"Dude!" Michelangelo exclaimed in a low voice as he leaned forward, not believing what he was seeing. "They're… they're ninjas!"

"What!" Raphael and Leonardo asked in equally surprised whispers and turned their heads at their siblings' direction.

"What you heard, guys. We'll be dealing with ninjas." Donatello shrugged. "Though that's not the odd thing about them. While using the thermal imaging feature on my goggles, I found out that their body temperature does not correspond to that of a human's. It's much, much lower."

His brothers gave him funny looks —Michelangelo with the goggles still on his eyes—, and the purple-clad turtle could almost hear the 'And we should care because…?' question that had surely popped up on their minds. He was about to give them a detailed, informative and very educational explanation about why that fact was important, but Raphael cut him off before a word could escape from his mouth.

"I just wanna know if that's something important for the fight or not, Donnie!"

The genius looked at his older brother, unfazed, as he retrieved his goggles.

"I can't tell for sure—"

"Great. I'll take that as a 'No'. Come on, guys!" Raphael said as he jumped into action and lunged at the figures. Leonardo made a quick motion with his head towards the tunnel, a clear invitation for his younger sibling to follow him and do a coordinated attack. Michelangelo accepted with an enthusiastic nod and both of them followed their eldest with a grin on their faces.

Donatello stayed in the back for a few seconds, shaking his head in amusement and thinking about his brothers' antics, before he began moving too.

Ah, brothers.

Inside of the tunnel there was almost no light.

Almost.

At ten yards from the entrance, there was a vault formed on the upper part of the tunnel. This vault was relatively small when compared with the surrounding infrastucture and it could easily go unnoticed if it were left in complete darkness. However, in that particular moment, the faint, small flickering orange light that was glowing weakly in its center gave right away the position of such perfect hiding spot to anyone who were paying enough attention to every darn feature of the tunnel.

Not that it really mattered to the figure who was standing on one of the beams that criss-crossed the vault, though. Since there weren't any beings other than his ninjas and he himself in that abandonded passage, he didn't have to worry about revealing his current position.

Arms crossed in front of his chest and surrounded by an impassive aura —despite the frown on his face—, the figure continued supervising every single movement his ninjas were doing, knowing that nothing could escape his eyes from up there.

Good. Everything was going according to the plan. While some of his ninjas were transporting the stolen material through the tunnel and the portal that led to the Underground, others were coming out from it and were heading to the outside to get some more. Soon, his ninjas would have gathered everything the Master had instructed them to get for his plan and the figure couldn't help but think about how pleased his lord was going to be when he heard the results of this mission.

Suddenly, the movements of his ninjas changed, and the figure instantly directed all of his attention to them.

Something wasn't right.

Instead of moving swiftly and in a well-organized way —like they were supposed to—, his minions were now moving erratically, as if someone or something were disturbing them and didn't let them carry out their job properly.

His gaze followed the lines of his ninjas, trying to find the reason of such change in their behavior. There, at the entrance of the tunnel, some kind of turmoil was taking place, but he couldn't see what exactly was happening in there.

He narrowed his eyes and his frown deepened even more.

Nothing, absolutely nothing, was going to turn this mission into a failure. Not now and definitely not on his watch.

He analyzed the situation in order to decide his next move. On one hand, the entrance to the Underground was to never leave his sight, so he couldn't personally go to where the turmoil was. On the other hand, he needed to find out what was causing such trouble in his lines so that he could take action on the matter.

He briefly pondered this before a solution came up to his mind. Well, there was a way to know what exactly was happening without him abandoning his current position, although it wasn't like he was very fond of resorting to that particular option. Nonetheless, he raised an arm and summoned the Shadows, the widely-known grand masters of stealth and espionage who had an incomparable ability to retrieve information without being detected.

From the corner of his eye, he could see the familiar pair of black blurrs creeping up the tunnel's walls and ceiling, and a ghost of a smile appeared on his face.

The Shadows had quickly answered his call.

With an energetic motion of his hand, he gave them a silent order:

'Go. Find out the cause of the commotion in my lines.'

And as one, the Shadows would start moving at his command.

Or at least that was what they were supposed to do, because in that very moment the Shadows were already on the move and had almost reached the entrance. A fact that meant his instruction had been rather pointless.

Ugh. Once again, their ability to anticipate orders had made them jump into action even before they were instructed to do so. A quality highly appreciated by the Master, but not by him. Never by him. On the contrary, that specific trait of the Shadows irked him a lot, because it usually let them be one step ahead of him, and, worst of all, it was their subtle way of defying his —and pretty much everyone else's— authority. However, he couldn't openly complain about it because it had been proven to be quite useful countless of times.

He stopped that train of thought when a pair of red eyes showed up in front of him. As usual, only one of the Shadows had returned to deliver the information, while the other kept assessing the situation.

Strangers, fighting the ninjas. Came the soundless report in the characteristic way of the Shadows to convey messages. Skilled, but without much experience in real combat. Might slowdown the mission.

Strangers, huh? An evil smile crossed his face as the figure allowed himself to enjoy for a few moments the mental image of him getting rid of the nuisances who had dared to interfere with his task. Unfortunately, his Master had made it very clear that the mission had to be carried out without drawing unnecessary attention from the people of the surface. After all, the Underground was to remain as a secret, at least for now.

So, would killing those outsiders attract unnecessary attention? Yeah, it certainly would, but oh, how much he would enjoy it! However, he didn't want to be held responsible of prying eyes going down there and accidentally finding the way to the Underground. No, he wouldn't allow it. He just couldn't allow it. That was the reason why he had ordered his ninjas to flee and not engage in combat if anyone tried to stop them.

Having considered all of this, the skilled warrior made up his mind. The material was going to be delivered no matter what, and the outsiders were going to be lead away from that place.

There was no time to waste.

He leapt from the beam and landed soundlessly on the ground. He looked around to see all of his minions before he made a sign with his hand and, immediately, all of the ninjas that were carrying material sped up their pace and began disappearing through the entrance of the hidden world. Then, the warrior gave other silent instructions to the rest of his minions.

'Block the outsiders until our cargo is safe and lure them away from here. Then, spread out and disappear.'

In the blink of an eye, a swarm of ninjas started moving towards the entryway with agile movements and the warrior just spared them a glance before a thought crossed his mind.

Supplies. He had planned getting more supplies for his army because the next part of his Master's plan was going to be carried out soon. He wasn't going to have enough time to gather everything if they didn't get at least some of them that day.

He weighed his options and decided he could take a slight risk in order to gather what he needed. He took out a small, pellet-like object from his clothes and threw it to the ground. A thin curtain of smoke appeared before him and when it dissipated another group of ninjas was found standing in front of him.

'Retrieve supplies for the army and leave no evidence of your presence,' were the default commands he always gave out, but since this time the circumstances required it, he found himself giving additional instructions. 'If necessary, engage in combat, but only on the surface. And if anyone follows you up to this point of the underground, then...'

He stopped for a brief moment while he considered if he should give the last order or not, but in the end, he made a final motion with his hand.

'Eliminate them. This time, no witnesses can be left alive.'

The ninjas bowed slightly and then they began moving. The warrior saw them blend with the bigger group of ninjas before he turned around and headed to the Underground.

When he had almost reached the entryway to the secret world, he felt the Shadows' gazes on the back of his head. They were following each of his movements as if they were expecting him to do something else.

He gritted his teeth. What did they want now?

He was about to turn his head towards the Shadows, when both of them presented themselves before him.

Get rid of the strangers. Now. One of them told him without a single word.

It wasn't an advice, nor a suggestion. It was an order.

The warrior, despite feeling annoyed because he had received an order from them, continued walking, not showing any kind of emotion and blatantly ignoring the Shadow's command.

Now. Pressed the other Shadow.

In that moment, he stopped in his tracks and turned his head towards them.

Oh, so they wanted to give orders to him? Well, then he would have to remind them who was in charge.

The warrior raised a hand and turned it into a fist, commanding them to return to the Underground. He inwardly rejoiced when he felt the Shadows shifting with unease and irritation, as if they were debating whether to disobey the direct order or not. He was certain that if they decided to ignore his instruction, they still wouldn't be able to do anything because, even if they were the Eyes and Ears of the Master, they didn't have any authority over his ninjas and they lacked the necessary fighting skills to engage in combat.

The Shadows hesistated for a brief moment, but in the end they decided to obey, as he had expected. He saw them pass next to him in the form of a blurr, heading to the Underground, not without giving him a final warning.

Fine. You'll regret it.

The warrior let a smile cross his face as he stepped down to the Underground and made the entrance to the secret world disappear.

No. Of course, he would not.

Meanwhile, on the outside of the tunnel, the turtle brothers were trying to fight a bunch of highly-annoying, seemingly-coward, elusive ninjas.

Big emphasis on trying.

After jumping into action, the brothers had tried to follow the pretty obvious winner option of Raphael's Great-And-Thoroughly-Thought-Plan-To-Find-Out-What-Those-Strange-People-Were-Doing-In-The-Sewers: Option B, punch first and ask later. A quite simple plan that only required them to wield their weapons with mastery and to throw several kicks and blows. No big problem. They knew how to do that.

However, had Option B been successful at stopping the criminals? No, not in the bare minimum, because, truth be told, the siblings hadn't been able to deliver one single strike to their opponents.

Why? Well, the blame could fall on one simple fact. Instead of making a counterattack after finding themselves caught under a surprise attack —like all proper villains would do—, the ninjas seemed reluctant to fight back and were only avoiding the blows.

Figures. Some criminals.

Nonetheless, the siblings kept trying to stop the thieves.

Michelangelo lashed out his kusari fundo, aiming for one of the ninjas who were carrying a metal piece, but missed him just for a few inches because the rascal had sensed the attack and had moved out of the weapon's way.

The young turtle made a pout before he swirled his kusari fundo again. The next time, he wouldn't miss!

Only that, well, he did.

"Is it just me or these dudes are really difficult to hit?" Michelangelo asked loudly as he swirled his weapon and tried to strike another opponent, but failing. "Hey, Leo, how many have you already managed to hit?"

"Counting this one?" the blue-clad turtle said as he swung his odachi towards a ninja that jumped backwards in order to avoid being struck. "Not even one. How about you, guys?"

"Haven't had any luck so far," Donatello answered at the same time he swiftly moved his techno staff to right and left, noticing that their opponents were moving faster than before.

"They… are… such… cowards!" Raphael grunted, marking each word with a punch that unfortunately didn't connect with any thief, while his mind tried to come up with another plan. "Okay, guys! This isn't working! We need to…"

He didn't finish his sentence. The sudden sounds of lots of feet coming from the tunnel had gotten all of his attention and he tensed his muscles, anticipating the upcoming battle. His brothers, after hearing those noises too, gathered around their leader and prepared for combat.

They didn't have to wait for too long before an incredible amount of ninjas came out from the tunnel and positioned themselves between the tunnel and the turtles, assuming stances that clearly showed they were more than ready to attack.

"Be ready, guys. And stand your ground," Raphael muttered to his brothers as he surveyed the ninjas who were now looking intently at them, not moving at all.

The tension grew between the ninjas and the brothers. Both groups stood still for a few moments that felt like an eternity.

And then, the ninjas lunged.

Author's note:

Thank you to everyone who has read this story! I hope you have liked this chapter so far!

About the story: As I already said in the disclaimer, this story is heavily based on the teaser trailer and the "Behind the Scenes" of the upcoming Rise of the TMNT. (It's my own way to share my excitement for the new show! Yay!). It's a 2018 AU, since the actual show hasn't aired yet.

About the Shadows: I don't know if they're gonna be actual characters of the show or not. If they are, they might have different abilities and/or roles than the ones I've given to them in this story. And if they are not... well, they exist in this story. All I can say is that the idea of the Shadows came up to my mind after seeing a little detail in the teaser trailer.

Author's babbling note:

You were not supposed to be my first published fanfic, but you are.

And you were supposed to be a one-shot fic, but you are not.

Thank you for teaching me that life is full of unexpected things, First Chapter-san. You're wise beyond your word count. /bows respectfully/