Author's Note: I hope the prologue didn't bore you. I promise you, things will escalate quite rapidly from here on. ;) And please keep an eye out for any goofy grammar or just plain weird English. By fixing the problems, more people can enjoy the story, and it will also improve my writing. So let me know if you find anything odd in the text. :)

TRIVIA: Not so "fun" fact: I had a panic attack while writing this thing. A full blown "OMG I'm dying and I'm gonna die and there's no tomorrow"-moment. I'm not sure why it happened. I've never had one before. But now I can't look at this story without thinking about it. Hopefully, none of you who reads this will ever have to experience what that feels like. But if you have: Here's a cookie and a hug. ^^

Chapter 1: "Try not to scream"

Leo's smile dropped as he left the dojo, and saw Raph sitting in front of the TV. His brother turned around at Leo's presence and gave him a victorious smile. Or a mocking one. Raph rarely made any difference between the two.

"Of course," Leo stated unimpressed as he walked up to the couch. "I told you that I wanted the TV after practice, so naturally you had to take it."

"And I told you that you could have it if you beat me," Raph informed him simply, and waved the TV remote at his brother with a grin. "Look how that turned out."

"I never agreed to that bet!" Leo exclaimed, with an upset gesture.

"Never said you had to." Raph shrugged.

Leo clenched his fists and glared at Raph. The other turtle grinned and eagerly took this as a challenge. He tossed the remote so that it ended up right between them. Leo looked from the discarded remote to Raph. His brother was smiling in a plotting way as he took on a fighting position, like a fox ready to catch a vole.

"Go on, take it," Raph coaxed, his legs like coiled springs, ready to jump at slightest of movement. "I'm up for a second round. Who knows? Maybe you won't lose horribly this time."

"Probably not," Leo stated, and calmly sat down in the couch where he picked up an old comic book instead. Without dignifying his brother or the remote a look. "Since I'm not gonna fight you."

"What the…?" Raph said with an upset look, and turned to Leo as if he had just insulted his mother. "Oh come on! You can't give me a walkover. I was just getting started here!"

"We just finished in the dojo," Leo explained, with a raised eyebrow at the quarrelsome turtle. "We've just had a backbreaking training session, and you still need to blow off steam? How can you not be tired of this?"

"Don't know," Raph answered, and folded his arms with a provocative look. "Were you guys wimpier than usual?"

"I'm not gonna fight you over the TV," Leo stated, ignoring the insult and flipped through the pages of the comic. He was just about to read it when he felt something hard hit him in the head and land in his lap. He picked up the remote control with a narrow look at his brother, who had sat down in the couch next to him and seemed too busy watching a commercial about air conditioners.

"Sometimes, I have my doubts that we are the same age," Leo thought out loud.

"Sometimes I doubt we're related," Raph pointed out casually.

Leo rolled his eyes at the comment, but then looked down at the remote in his lap and picked it up with a pleased smile. He aimed it at the TV to switch the channel, but his expression changed when the remote didn't want to comply with the order. He tried the buttons several times and then gave Raph an annoyed glare.

"Just so you know, this just proved my theory," he told him.

"What did?" Raph asked, with a frown.

Leo didn't elaborate. Instead, he bitterly opened the battery hatch and showed his brother the empty compartment.

"Don't look at me," Raph said, and shook his head. "My kind of pranks has more carnage to them. This kind of immaturity is more Mikey's thing."

"Wait, where is Mikey, by the way?" Leo suddenly asked and looked around, as if he expected the youngest turtle to have been quietly observing them the whole time. He felt ridiculous for even considering the idea.

"Why don't you ask the B-team's better half?" Raph suggested, and turned his attention back to the TV.

"You mean Mr Distracted?" Leo said, with a crooked smile. "I doubt Donnie knows where he is. He could barely keep an eye on Mikey during training. Which is quite an achievement considering that his nunchuks were in his face most of the time..."

"So you noticed it too, huh?" Raph asked, with a glance at Leo and chuckled. "Man, he really didn't put up much of a fight today. I think I still can see his face in my knuckles."

"You could have gone a little easier on him," Leo told him, knowing that his words fell upon deaf ears. "But you're right. Donnie did not have his head in the game today. I thought it was odd that Sensei called off the training so early, but now it kinda makes sense…"

"Yeah, maybe he realized that when one of your students is turning as purple as his bandana, it's probably a good time to quit," Raph said, with an amused grin.

"When I think about it, I've barely even seen Donnie today," Leo admitted with a thoughtful expression. "Not before the training anyway."

"I have," Raph shared, with an indifferent look. "Those twelve seconds at lunch when he grabbed the toaster and a couple of forks. Not food, just the toaster and forks."

"…Should we keep a better track of what that guy does in his lab?" Leo said, with an almost worried look. "He's been more antisocial than usual today, and we have literally no idea what he's doing. One second we only see him when we train or eat, and the next second he has made smoke bombs, t-phones, go-karts-"

"Patrol buggies," Raph corrected him, just to annoy.

"What I'm trying to say is that he's been cooped up in the lab for too long," Leo said and got up on his feet. "I know that we need the retro-mutagen, but I think he needs to get away from all that work. It can't be good for him."

"Yeah, someone should totally tell him that," Raph agreed with a petty wave, indicating that even though it was his idea, he didn't care enough to act upon it. Leo made a little sigh at Raph's lack of interest, but shrugged it off and went to the lab.

As expected, the purple clad turtle was occupied with various kinds of projects. The whole lab seemed to be unusually crowded with stuff, and Leo got a strong feeling that Donnie must have made a trip to the junkyard very recently. He had no idea when Donnie had the time to do it, or even what he needed all the stuff for. Most of the things looked completely unrelated to each other. He could only imagine why Donnie would need an ironing board, where most of the padding seemed to have been chewed off. They didn't even own an iron. Or clothes, for that matter.

Leo tried his best to not trip over any wires or objects as he made his way through the mined area. The scientist was fiddling with a gadget that could barely be distinguished from all the tech bits and different colored cords that were attached to it. Donnie's tongue was sticking out in concentration while he tried to reach something through the cable-convention with a screwdriver.

"Hey Donnie," Leo announced, when he was close enough for a proper greeting. "Sorry to bother you, but... Have you seen Mikey?"

"Not since practice," Donnie answered without looking up, and picked up another screwdriver to assist the first one. "Why? What did he do this time?"

"Actually, he hasn't done anything," Leo said, and sounded surprised over his own statement. "Except for apparently finding a new home for a couple of triple-A batteries…"

"Uh huh," Donnie answered vaguely, his eyes fixed on the contraption before him. "I'm not sure if I'm following you here… Did you want to ask him something?"

"No, I just want to know where he is," Leo said with a shrug. "The thing with Mikey is that whenever he's doing something on his own, it's rarely something good. Especially for us. It tends to be related to new recipes, or water balloons with our names on them... Either way, I'd prefer to have a heads up so that I can take cover."

He gave Donnie a crooked smile, but his brother didn't pay him any attention. Leo observed him for a moment, before walking up to desk.

"So," Leo started a bit uncertainly, with a wary look at a jar of boiling ooze on the desk right next to Donnie. "are you getting any closer to finding a retro-mutagen?"

"Does it look that way from how I barely can contain my excitement?" Donnie replied bitterly, unscrewing something from the device's insides.

"Sounds like someone didn't sleep well last night," Leo pointed out, and folded his arms with a narrow look.

"Actually, I didn't sleep at all," Donnie corrected him.

Leo chuckled at Donnie's answer, as if it was meant as a joke, but went quiet when he noticed the drained look in the other turtle's eyes.

"Wait, you're serious?" Leo asked, in disbelief. "Donnie, that can't possibly be good for you, and you know it. You can't keep this up-"

"I'm not tired," Donnie told him casually, as he studied the device in his hand, almost as if he was trying to recall what he needed it for now again.

"Right," Leo said, with a doubtful look. "Well, at least this would explain why you've been so... gloomy all day."

"Gloomy?" Donnie asked, in surprise, and turned to Leo with a raised eyebrow. "I'm not gloomy. What makes you think I'm gloomy?"

"Except from the fact that you've kept to yourself all day and barely talked to us?" Leo asked, and leaned on the desk. "And that you let Mikey completely own you in the dojo earlier. I'm telling you. That was painful to even watch. You didn't exactly make it hard for him. Or any of us for that matter…"

Donnie looked as if he wanted to protest again, but hesitated with an uncertain look. His expression suddenly changed into a dejected one and he let his head fall back with a tired groan. He gave the screwdriver a look before he let it drop to the desk. Leo watched his brother with a concerned look.

"Is there anything you wanna talk about…?" Leo asked, and folded his arms. "I don't mean to sound bossy, but you seriously need a break."

"Okay, so maybe my mind has been a little… Occupied lately," he apologized, and put the wire-device aside as if he was done tinkering with it for the day. "It's just... I really thought I was getting closer last night. It's like I got all the pieces right here in front of me, but I can't see what the puzzle is supposed to look like. It's very frustrating, and I still have no idea how to solve it."

"I see," Leo nodded, with a sympathetic glance at the struggling scientist. "Look, don't be so hard on yourself. Nobody's is asking you to come up with a cure overnight."

"… But within a year would nice," Donnie mumbled to himself.

"Donnie, listen," Leo said, and put a hand on his brother's shoulder. "Beating yourself up isn't gonna help anyone. Just take the time you need, get some proper sleep, and you'll eventually figure it out."

"Eventually isn't fast enough." Donnie shook his head, with a depressed look.

Leo observed Donnie for a moment, but wasn't sure what to say to cheer him up.

"...I wish there was something I could do to help," Leo said sincerely.

"There is."

Leo turned to Donnie in surprise, not expecting his brother to take him up on his offer right away. Donnie watched him with interest for a couple of seconds before pointing to a small, handle-shaped gadget on a nearby table. The shape indicated that it once might have originated from the handle bar of a bicycle, and a car battery.

"Could you grab that for me?"

"… Sure." Leo agreed, and couldn't quite figure out why he hesitated.

He walked over to the table and picked up the object in question.

Pain.

Leo gasped as the electrical current ran through his fingers and down to his feet, frying every muscle on the way. The numbing feeling spread like a wildfire through every inch of his body, disabling every limb. Leo could feel his legs buckle against his will, and how his body fell to the floor. He landed heavily on his stomach. His brain felt so paralyzed that he wasn't sure whether it had hurt or not.

He could feel his consciousness drifting. Leo desperately tried to move his arms, but he could barely feel them anymore. His vision was getting blurred. Leo managed to raise his head somewhat, and his eyes fell on Donnie's feet. He had his bō by his side, and were standing right next to him. Leo opened his mouth to say something when he felt a something hard strike him over the head. The sharp pain was the last thing he felt.

"Leo? Can you hear me?"

The voice felt unnaturally distant. Leo couldn't tell if it belonged to a forgotten dream or reality. His head hurt pretty badly though, so maybe that had something to do with it…

"… Donnie?" Leo mumbled in a dazed manner, not entirely convinced that it was his brother's voice he'd heard. It felt like all his senses were just getting back online after a major reboot. His brain tried to recover the lost memories, while his eyes struggled with the art of distinguishing shapes.

"It's okay. I'm right here, buddy," Donnie said reassuringly. "Everything is alright."

"No, I'm… I'm not…" Leo began hazily, as he slowly started to recognize the familiar surroundings of the lab. Something wasn't right. How did he hurt his head now again…? "… Wait, w-what did you-"

Leo's mind suddenly became wide awake when he realized that he couldn't move his arm. He turned his head to see what the problem was, only to discover that he was strapped down to a table. His arms, legs, and even chest were restrained with what seemed to be old, mismatched seat-belts. He stared at his tied down body in utter disbelief, and looked around for a context to the situation. His eyes landed on Donnie, who was standing right next to Leo's head. The purple clad turtle was quietly observing Leo, his curious eyes a little too close than Leo found comfortable. He noticed that Donnie was wearing his goggles on his forehead, along with a white lab-coat Leo didn't even knew that the turtle owned.

"… Donnie," Leo began calmly, while his arms violently yanked at the restraints. "What is this...?"

"Easy, easy," Donnie instructed soothingly and made a nonthreatening gesture, like when you try to calm down an agitated animal. "There's no need to freak out. You have just been secured to a table, okay? Everything is perfectly fine."

"That's not the definition of fine," Leo explained, with a strained voice as he desperately tugged at the belts, but the tight straps prevented him from even twitching. "That's everything but fine. What the heck is going on?"

"Well..." Donnie pondered, and curiously looked at the mess of experiments and junkyard trash around them. "A lot of things, to be perfectly honest. You're gonna have to be way more specific if you-"

"Why am I tied up!?" Leo interrupted, with a frustrated glare.

"Oh. Right," Donnie said, as if he hadn't been aware of Leo's predicament until just now. "Okay, the short version is that I think I've finally made some progress in my mutagen research."

"And the long version?" Leo asked, and tried his best not to yell the question.

Donnie didn't reply immediately. Leo felt how a hand brushed by his head as the turtle walked around him to get to his working desk. He leaned towards it in a contemplative way, before looking up with a fascinated look.

"Have you ever considered how absolutely incredible we are?"

"... I think Raph spends an hour a day doing it," Leo answered truthfully.

"The one thing we know for sure about mutagen is that it's extremely unpredictable," Donnie continued, and started fiddling with some test tubes containing a red substance. "Whether it's humans, animals, or plants, it's nearly impossible to predict what the mutation process is gonna do to the subject once it's been exposed. That inconsistency is the main reason why it's so difficult to come up with a way of reversing the effects. Every case is so unique that it's hard to calculate how mutagen really works."

"... And?" Leo asked, with an uninterested look.

"And, that made me realize something," Donnie explained, with a victorious expression, not unlike that of someone who had just figured out how to cheat in a game. "I happen to be in the rare position of having, not one, but three mutants with the exact same kind of mutation as a result from mutagen exposure. If I conduct a more thorough study on your physiology, I could unlock the secret on how mutagen affects different individuals and species!"

Donnie smiled as if he had finished a successful presentation and expected applause. But Leo just blinked at his brother with big eyes, similar to someone who was slowly realizing that he's swimming in shark water.

"You're kidding, right?" Leo said, with a wary look at the other turtle, hoping that he had misunderstood. "Donnie, you're not experimenting on us."

"Actually, I am experimenting," Donnie corrected, and showed Leo the swirling content in the test tube he was holding. "I took this sample from you to study how your DNA reacts with my attempted retro-mutagen. I discovered that using mutated blood is by far the best way to determine if the retro-mutagen is working the way it should. I can't believe that I've never even considered doing this before..."

Leo's pupils were as small as pins as he observed this strange version of his brother, and the way he with great interest studied Leo's blood in his hand. The straps around Leo's chest felt somehow tighter than before. He really wanted this to be a prank. A hilarious practical joke by a guy who usually made puns about chemical symbols. But somewhere in Leo's mind, he knew that this had gone way too far for that.

"Donnie," he began, with a hollow voice. "Something... is very, very wrong with you."

"No, I'm fine," Donnie assured him simply, as if Leo just had asked him about his day. "But your sample looks a bit iffy... It doesn't seem to respond to my concoction at all."

"This is insane!" Leo exclaimed upset, and stretched the belts to their limits. He didn't care that it hurt. "Donnie, take these things off me and let me go! I'm not gonna help you with this!"

Donnie looked up from the vial of blood and observed Leo with a thoughtful expression, as if he was trying to figure out why his brother was so upset. He put down the sample and walked over to Leo's table. The older turtle turned away uncomfortably when Donnie leaned closer to his face and studied him with a curious look. Leo felt a nervous tug in his stomach. Was Donnie trying to diagnose him…?

"… I think I understand the problem," Donnie finally concluded with a serious look, and jumped over to a cardboard box on the floor next to the working desk. "But don't worry! I know exactly what you need…"

Leo didn't want to know what Donnie thought he needed. Donnie had already strapped him down to a table and, apparently, drawn a significant amount of blood from him while he was still out cold. Leo had no interest in finding out what Donnie had in store, but he knew one thing: It wasn't going to be pleasant. Not for him.

"Found it!"

Leo closed his eyes tightly. He couldn't move his arms. He couldn't move his legs. He was completely immobilized. But whatever Donnie was planning to do to him, he could at least choose not to watch.

"Okay… That's not very helpful," Donnie stated, unimpressed. "Open your eyes now, Leo."

Leo refused.

"Come on, what do you think I'm gonna do to you?" Donnie said, with a disapproving voice. "Don't be ridiculous, open your eyes. I think you're gonna like this."

Leo highly doubted that.

"Ah, I see…" Donnie suddenly said in a softer voice, and Leo flinched when he felt a comforting pat on his chest. "There's nothing to be afraid of. I'm just gonna give you something that will make you feel better. It's not something bad, I promise."

Leo shut his eyes even tighter, just in case his crazy brother would try to pry them open. After a minute, a sudden faint scent reached his nose, making the blue clad turtle raise an eyebrow in surprise. It smelled… sweet?

He finally opened his eyes, only to find a red lollipop one inch away from his face. Leo stared at the candy as if it just had started singing "Happy birthday to you", and then stared at Donnie. The scientist was still standing next to him, offering him the candy with one hand, while holding a whole jar of the stuff in his other. He looked at Leo expectantly.

"Lollipop?" Donnie offered.

"What…?" Leo asked, in disbelief.

"Here," Donnie insisted, and poked Leo lightly with it. "Have one."

"Where the heck did you even get those?" Leo wanted to know, and looked back and forth between the lollipop and Donnie.

"Same place I got most of this stuff," Donnie answered, and looked from the various bottles on the desk to his new lab coat.

"… When did you have the time to rob a hospital?" Leo asked, with a wary look at his brother.

"I haven't 'robbed' any hospital, thank you very much…" Donnie said with an offended look, and put the lollipop in his pocket. "These things belong to a private clinic a couple of blocks from here. Or, I suppose 'did belong' is a more accurate conjugation since they… Well… Don't have them anymore."

Donnie made a small awkward laugh at his own remark, as if the thought hadn't occurred to him until just now.

"Great. So you've only robbed a private clinic then," Leo stated sarcastically.

"I had to. I doubt that they would just give me the stuff," Donnie simply explained, and went over to the desk where he put down the jar of sweets and picked up a bottle instead. He studied the label with an intrigued look. "… and some of these things are kinda expensive."

"What else did you take?" Leo asked, with a serious look.

"A little of this, and a little of that…" Donnie answered vaguely, without looking up from the bottle. "… and then some."

"And none of this sounds wrong to you?" Leo asked in surprise.

Donnie moved his focus from the flask in his hand to Leo instead. He watched him silently with a puzzled look, as if he thought that Leo's question was very odd and wanted him to elaborate. Leo rolled his eyes in annoyance before looking up at his brother again.

"Donnie, this has to stop," Leo said, with authority. "You're not acting like yourself. You must have noticed that."

"Well, now when you're mentioning it…" Donnie admitted, with a thoughtful expression, which quickly changed into a confused one. "… Actually, no. I'm not sure what you're getting at."

"You tied me to a table!" Leo pointed out, and tugged at the straps to prove his point.

"Leo. It's for your own good," Donnie explained calmly, and put down the bottle. "We have a lot of procedures ahead of us, and many of them require the specimen to remain very still-"

"Specimen? We're you're brothers!" Leo protested. "I'm not sure what has happened to you, but it has to be something pretty bad if you're seriously considering doing this to your own-"

Leo didn't finish the sentence. He stared at Donnie in sudden realization, with an unnerving feeling crawling inside of him.

"… What have you done to Mikey?" he asked. The table felt strangely cold on his skin.

"Let me get back to you on that," Donnie replied as he put aside a couple of test tubes, and picked up a large syringe instead. "I need some more samples first so that I can finish the test properly."

"What?" Leo asked with a confused look, which was immediately replaced by a terrified one as Donnie approached him with the medical tool. "Whoa, whoa, hold on a second here! No, no. Stop it, hey- OW!"

Donnie didn't even hesitate before he plunged the sharp instrument into Leo's arm and penetrated the skin. Leo cringed in pain and watched the glass barrel fill up with red as Donnie slowly pulled the plunger. The view made him feel nauseous, and caused him to involuntarily look away as his brother retracted the needle from his flesh.

"There! Perfect," Donnie announced as he held the instrument up in the light, but then scratched his chin uncertainly. "...In retrospect, I should probably have gone with the 100 milliliter instead. I'm gonna need way more than this if I wanna do a sufficient amount of tests today. Why don't we have any vacutainers...?"

"Splinter is gonna find out about this," Leo pointed out, with a narrow look at the tiny puncture wound on his arm, wishing that he could rub off the stinging sensation. "You know that, right?"

"I'm not sure he will," Donnie commented absently, as he went back to his desk while swirling the sample above his head. "He drank a lot of tea..."

"What's that supposed to mean?" Leo asked, with a raised eyebrow.

"That I'm glad I was the only one who volunteered to make breakfast," Donnie explained casually, as he added the blood sample to a vial with a clear liquid.

Leo felt a shiver run down his spine, as he realized that there might have been another reason to why their sensei had decided to end their training sessions prematurely. Leo could suddenly feel how his worry was slowly being replaced by something else. It felt like fear. Fear of what was going on with his brother, and fear of what he could do to their family in his current state. But what concerned Leo the most wasn't Donnie's actions alone, but the fact that he was still talking and behaving just like the real Donnie. As if everything was just normal.

What could have corrupted his mind so terribly that he didn't realize that this was wrong?

"Alright, that should do it," Donnie said in a low voice, as he put away the vial in an old mini-fridge, which was covered with partly removed stickers. "Now I just need to add the new data to my journal, and then I can check on the first batch to see if it's unchanged."

"Look, Donnie," Leo started, with an uneasy expression, not sure how he was supposed to reach out to him. "I get that you're under a lot of pressure. Especially after April's dad got mutated into… a sort of red bearded, bug eating, mutant bat. But the point is that you have to give yourself a break. I know how hard it must be for you to create a retro-mutagen, I do, but-"

"Sorry to interrupt, Leonardo," he stopped him, and turned to Leo. His face was suddenly very serious. "but I'm gonna go ahead and correct you right there. You have NO idea how hard it is for me to find a retro-mutagen. In fact, you have actually no comprehension whatsoever of the level of difficulty I am experiencing in my attempts to find ways to fight off this whole alien invasion."

"You make it sound like you're fighting against the Kraang all by yourself," Leo pointed out with a disapproving glare.

"Am I not?" Donnie asked, and tilted his head slightly in a wondering way. "I am the one who make all the gear we use, the one who's monitoring the Kraang's communication device, decrypting their codes, and trying to find a way to reverse the effects from their mutagen. How exactly are you guys contributing to that?"

"You know we are," Leo argued in frustration.

"And I can tell you how," Donnie added, and picked up a tray with surgical instruments from the desk and walked up to Leo. "You help me."

"... What are you doing?" Leo asked with a suspicious look at the tray, but he couldn't quite distinguish its contents from his awkward position.

"I need more information about how mutagen enhances natural abilities," Donnie informed him as he picked up an electric hand saw from the tray of equipment.

"What the heck is that thing?!" Leo exclaimed, and tried to lean as far away as he could from the machine.

"Something I wish was a rotary reciprocating saw..." Donnie admitted, with a critical look at the power tool, but then shrugged. "Let's call it that for now."

"Wait, wait, wait! W-what are you gonna do to me?" Leo panicked, as Donnie moved the saw closer to his body

"I'm testing the density of your shell structure," Donnie explained, as he gently stroked a spot on Leo's chest and then aimed the saw at it. "Just lie still, it'll be over in a few seconds."

"This isn't funny, Donnie!" Leo yelled and, despite the doctor's orders, desperately struggled against his restraints to get away. "Knock it off! I'm not gonna let you cut through my shell!"

"Relax," Donnie said reassuringly, and looked at Leo as if his brother was being very unreasonable. "The carapace and plastron only picks up pressure differences, they hardly contain any pain receptors at all."

"HARDLY!?"

"Pun not intended. Ok, here we go," he informed, as he put on his goggles and turned on the tool with a roaring sound. "Try not to scream."

Next time: Leo's in a bit of a pickle, but how far is Donnie really prepared to go? Also, we'll find out where Mikey has been during all this…

Author's Note: Okay, I need your help, guys. I WANT to keep writing on this story (especially on chapter 3…!), but the problem is that I'm also working on the new chapters of "That time of year again". I meant to finish that story first, but then this little fella' just showed up in the middle of everything…! In other words: I don't know which story to focus on right now.

So I really need to know what you guys think. Should I keep writing on this one? Would you like to read more?