Author's Note: 2012 universe, takes place after Season 4. Translated from my fic "Echange temporel".

Prologue

Leonardo bowed to his father's shrine. Splinter had died months ago, but it could as well have been yesterday for him. He missed him so much. They all did.

He sighed and straightened up. He was way too young to be Sensei, way too young to be responsible for an entire ninja clan - no matter how small it was.

Shredder hadn't left him any other choice.

Shaking his head, he decided that it was time to join his brothers. Their company prevented him from focusing on the past, and besides, he felt the need to enjoy a relaxing afternoon for once.

He left the dojo, instinctively bowing his head to avoid Michelangelo's skateboard, which was crossing the living room at high speed with said Michelangelo on it. Then he stepped aside to let Renet pass. The Assistant Time Master had become very close to his brother, which you wouldn't have guessed considering how furious she looked.

"Mikey! Come back at once, we're not done," she shouted, her hands grabbing the Time Scepter as if it was a club.

"I'm sorry! I'm really sorry!" Michelangelo had obviously no intent to stop, and Leonardo winced when he heard the creaking of abused furniture. Once again, the living room was going to be a mess.

Resigned, he walked to the couch where Raphael was watching the chase with the utmost interest. Leonardo sat down next to him.

"Do I want to know?"

Raphael nodded, grinning. "Mikey told her that he had never met a girl as old as she is, and that it was awesome."

"As beautiful, you mean?" Leonardo inquired.

"No, no, as old. He's probably right, mind you, but Renet took it the wrong way. That or she's very good at faking it."

Renet was running past the couch and winked at them. Leonardo shook his head.

"I see."

The distinctive sound of an explosion diverted his attention. It was coming from Donatello's lab, and Leonardo would have hurried to the room if he hadn't heard Donatello's disgusted exclamation. Nothing out of the ordinary, then; no reason to worry.

Leonardo folded his hands calmly as he heard cracks and clashes coming from the kitchen, where Renet's chase was going on. This was Michelangelo's favorite room in the lair and he would never damage it beyond repair.

A few seconds later, Michelangelo burst into the living room again, Renet after him. As they came closer to the couch, another explosion resounded, much stronger than the first. Leonardo frowned. This time, he was going to check on Donatello, and maybe veto this particular set of experiments. In one graceful move, he jumped above the couch, careful to avoid Michelangelo and Renet still running across the room…

A blinding light beam caught him mid-air. He let out a strangled cry and fell on the ground, all grace forgotten.

"Leo!" Raphael shouted, running to his brother.

Leonardo grunted and sat down, drawing his knees up to rest his head on them. Eyes closed, he massaged his head.

Raphael sighed in relief before turning to Renet, ready to jump down her throat.

"What was that?"

Renet took a careful step back. "I… uh… he surprised me, and I activated the Time Scepter. Don't worry, it wasn't set on time travels."

"We're lucky indeed." Raphael crossed his arms, not ready to be so easily soothed.

Luckily for Renet, Donatello chose this precise moment to leave his lab with his head down. His skin, which should have been a nice green, was now a bright purple. This effectively caught Raphael's attention.

"Don't ask." Donatello shook his head before noticing Leonardo on the ground. "What happened?"

Renet cleared her throat.

"The Time Scepter uses self-defense, and it's linked to its bearer's emotions. I… uh… I'm still learning the theory behind it."

"The Time Scepter can stun? Interesting," Donatello whispered.

"Don't get any ideas," Raphael grumbled.

Donatello ignored him to focus on Renet. The Assistant Time Master was apologizing to Leonardo, who was ignoring her completely. He was obviously still shell-shocked.

One of Renet's many watches rang, and she winced. "I have to go home if I don't want to be late. And believe me, I don't want to be late. Lord Simultaneous is a tyrant, I'm telling you." Shaking her head, she waved at the turtles. "See you later, Mikey! And sorry again about Leo."

"No problem, Renet!" Michelangelo's huge grin almost didn't waver when Raphael glared at him. "What?"

"That girl is a walking disaster."

"Like you're not a walking disaster." Michelangelo crossed his arms, ready to defend his friend.

On the ground, Leonardo was still stroking his head. With a last moan, he unfolded his body and stood up, looking at them. His eyes widened when he registered the state of the living room.

And his brothers froze.

"Guys, what happened? Master Splinter will be furious when he'll see that." Leonardo waved at the place, including Donatello-the-purple-turtle in his gesture.

Raphael opened his mouth, but no sound left it. Michelangelo raised his hand to hide his. Donatello lifted a finger, his questioning face showing that he wasn't sure he had heard his brother correctly.

"Master Splinter?" he said weakly.

Leonardo tilted his head.

"Well, you know. A giant rat. A ninja master. Our Sensei?"

His tone was clearly sarcastic, and Raphael let out a strangled cry, very unworthy of the powerful warrior he was. Donatello nodded, assessing the situation. Leonardo shouldn't have had this voice, the voice he had before Shredder almost killed him. He shouldn't have had this juvenile look either, without the scars their many battles had left on his skin and shell.

Granted, Renet had told them that the Time Scepter wasn't set on time travels. However, she wasn't always the most reliable person.

"Guys?" Leonardo was obviously wondering what he had said wrong. "What's the matter?"

Michelangelo took a deep breath and gave his brother a shaky smile. Raphael, still under shock, opened and closed his mouth again.

Donatello stepped forward and put a purple hand on his brother's shoulder. "Everything is fine, Leo," he said in a tone that meant the exact contrary. "By the way, how old are you?"

Leonardo smiled, a little incredulous. "I'm fifteen, of course. Like you three. Why are you asking, Donnie?"

Michelangelo was the first to break the following silence. "Well, we're almost there," he said encouragingly. "Four years aren't that big a deal, right?"

Raphael's fists clenched and unclenched convulsively. Obviously, he wasn't appreciating the joke.

"Call back Renet. Now."