Leo hauled himself out of the water and onto a concrete bank, gasping for air. He was trembling, pushed up on his hands and knees as he coughed up the liquid he inhaled.

'Breathe, Leo breathe,' he commanded himself. 'Just like sensei Tsuyoi taught you… Great, six fingers. I'm hallucinating.'

He squinted down at his hands, willing himself to see clearly. When he still couldn't see more than three fingers on each hand, he sighed, flopping down to rest on his stomach. The feeling he had felt in the tunnel had evaporated now, replaced by a skull-splitting headache. His body felt numb and cold and he just wanted to curl up and take a nap…

He snapped his eyes open at the thought, sitting up quickly. Taking a nap after nearly drowning sounded like a free pass to death, and Leo stood on shaky legs. He needed to find the others, get out of here and get help.

How did he get down here anyways? He remembered an earthquake and a crack splitting open between the rails, but a cursory study of the ceiling showed no scars or flaws. Just the dull, curved roof of what seemed to be a large sewer tunnel. 'Actually,' Leo thought with a slight smile. 'It's more like an underground lake.' He must have drifted downstream from where he fell, and Leo was just grateful the water looked clear, if a little… glowy.

Eyeing the sidewalk-like edges of the tunnel, Leo decided that they were his best bet out of this place. He stretched his legs and then his arms, trying to get feeling back into his limbs. However, when he tried flexing an arm over his back, something blocked the complete movement of his shoulder blade. Leo frowned, rolling his shoulder again slowly. Once more, he felt a slight resistance of something firm against his arm.

Leo twisted, trying to see what he kept bumping into. He spun in circles, chasing whatever it was like a dog chasing his tail and a cold feeling of dread settled in his chest. No matter what, it was stuck on his back, and all the feeling he managed to get was telling him it's staying for good.

Leo stopped trying to grab at it, focusing on breathing evenly. So far, it was proving to be a very difficult task to keep from panicking. He just had to know what it was. Carefully, Leo reached behind himself, ignoring that faint tug on his shoulder. He brushed his fingertips along his back, inspecting the object.

It was a curved shape, but not too bulky as to constrict movement, and it felt vaguely like there was a ridge surrounding it. The inner surface felt much like a puzzle of hexagons, each connecting to form the convex material. It felt firm and solid, too. Leo bit his tongue, a memory of one of his teacher's class pets surfacing in his mind. It felt like a-

The sound of violent splashing and a sputtering sound snapped Leo out of his confusion, and he jerked around to look at the water's edge. A hand had thrust from the water, grasping at the concrete ledge. A head followed, appearing as a faint smudge in the weak lighting.

Leo rushed over, grabbing the wrist to haul the person from the water. He was sure it had to be one of the others; Leo doubted that there would be anyone else swimming down here, let alone voluntarily. Another hand snaked from the water, taking hold of his free hand, and Leo pulled him onto the concrete with a grunt of effort. He sat on the ground with an exhausted sigh a few feet away from his rescued companion. Whichever one of the boys he pulled out needed to lose some weight!

"You okay?" Leo asked when he caught his breath.

The other boy hissed, pulling into a sitting position.

"Think so… Just a little- What de heck!?"

The other boy, whose voice sounded like the redhead's, scrambled backwards into a shaft of pale light, pointing a shaky finger at Leo. Leo had jumped back in surprise, turning around quickly, trying to see what he was pointing at. A look of startled confusion crossed his face, and he looked back at the hothead with a look of worry.

He wasn't pointing at something behind Leo.

He was pointing at Leo.

Leo swallowed, slowly raising his shaking hands to inspect them. Slowly, he moved them into a small beam of dusty light. What he saw nearly made him choke.

His hands were green, and still had only three fingers. He reached up to touch his face, shock freezing his expression. He had no nose or ears, but he could still hear and smell. Looking over his body even more, Leo could see a firm-but-flexible, golden plate running across his front beneath his shirt. This… this was not normal. Leo was now truly and utterly afraid.

"What de heck are ya!?" The other boy shouted, and Leo nearly jumped out of his ivy skin. If the water was what had caused this, then…

He peered closer at the other boy, alarmed curiosity nipping at his mind. Now that he was in the light, Leo could see that the other's skin was a deep emerald, with the same features Leo noted on himself. Three fingers, tan plates, and a…

…shell.

"What are we?" Leo whispered in horror. The other boy looked down at himself fearfully, flinching in fear and hugging his chest when he saw that he too was no longer… human.

"What de heck happened to us!? We're… we're…"

"Turtles."

..::-::..

"Incredible!" Donnie said in awe, raising an olive arm to inspect the muscles that rippled beneath the skin. He had no idea what happened to make him, well, mutate like this. In fact, he hadn't even realized that he had changed until he pulled himself from the sewer water onto a jutting pipe thick enough to rest comfortably on.

"Strangely numb," Don muttered to himself, poking and prodding at his new body, "but amazing! Unless this isn't my body…" He tapped a finger against his front teeth, seeking out that tooth gap that he was always so embarrassed about. He used to get teased about it endlessly in middle school, and since then he had carefully hidden his toothy smiles to avoid further embarrassment.

He still had it in this form, apparently, which made him relieved and self-conscious at the same time. So he didn't somehow switch bodies with another creature, but instead his body was transmuted into a terrapin-humanoid. Donnie let out a quiet laugh, wondering if he was dreaming. Dreams could be vivid, but Donnie doubted they could this accurate. Plus, he had already pulled the pinch test, and even with his muted senses he had let out a whimper of pain.

The scientist in Donnie was itching to break through and rattle off numerous theories and tests, and he probably would have launched into a rant with himself if he didn't at least have some of his sanity.

'Right now,' he thought logically, 'I need to find Leo, Mikey and that other guy, see if they changed, too. I can move on from there, find out if this is linked with that earthquake, or something else entirely.'

He slid off of the pipeline into the knee-deep water, glad that it didn't look too putrid. This area was probably reserved for the storm drains. If he kept moving, there should be an exit somewhere ahead. He just hoped that the others weren't in any kind of trouble.

'But then again,' Donnie thought as he looked at the traces of a glowing green substance floating downstream. 'Maybe I should first find the source.'

So upstream it was.

..::-::..

"What da heck happened to us?" Leo's companion asked, his voice not yet rid of his panic. For a guy who had been so confident and arrogant just two hours ago, according to Leo's still-living wristwatch, he sure could revert to a frightened child pretty quickly. "Please tell me we ain't gonna stay like dis, man!"

"I don't know, okay." Leo sighed, exasperated as they walked down the sewer halls. This wasn't the first complaint the other made, and Leo could only wish it was the last. He couldn't focus on his fears at the same time he was trying to find a way out. "Look, let's just keep moving. The sooner we get out of here, the better off I'll feel." 'And the further away I'll be from you,' he mentally added.

The other growled, grabbing Leo's shoulder. He was almost able to stifle his surprised expression at the different anatomy this time. Almost.

"And den what? We walk the streets of New York an' just hope that we'll change back like some pretty fairy tale? Oh, no, Fearless, it ain't dat simple!"

Leo huffed, tugging his arm away. "Would you stop calling me that? My name is Leo." He turned to face him, crossing his arms over his… chest? Plastron? Breastplate? "And I don't suppose that after all that happened that you would be interested in sharing your name? Or do you just want to be called 'hothead'?"

He snorted, balling his hands into fists. "Fine, Leo," He spat. "Call me whatever de heck you want! As soon as I'm back ta normal, I don't hafta look at yer ugly mug anymore, and I'll be just another memory." He faltered a moment, confident mask slipping a little. "But… we don't have any idea how to reverse this, do we?" Leo's expression softened at his downbeat realization. The other boy invisibly shook off his depression, snarling as he pushed past Leonardo. "Jus' call me Raph, then. But don't think for a second that we're gonna be best buddies, or I'll crush your skull against the pavement!"

Leo smiled a little at that, walking in step behind him. "Raph, huh? That's an odd name…"

Raph growled in frustration. "It's short for Raphael, okay? Go ahead, make fun of me. I wanna see how well ya can function without a brain."

"No, no! It's cool!" Leo said, struggling to keep from laughing at Raph's defensiveness. "My name's short for Leonardo, after all."

"Deserve a medal for that, do ya?" They were walking side-by-side now, the walkway just wide enough for the both of them.

"No, just welcoming you into the fools-with-long-names club." Leo joked. He could see Raph was beginning to relax around him.

They turned into a side tunnel Leo pointed out and kept walking in silence. It felt like an hour had gone by before Raph spoke again.

"So… what are we gonna do about dis?" He asked, gesturing towards their changed bodies with an unsure expression. Leo felt his look waver, and he faltered in his steps.

"Honestly… I don't know."

Raph looked hopefully at him. "But dere's gotta be a way to reverse dis, right? We can't stay like this forever… and I'm hungry. What if I can't eat what I normally do?"

"I'm sure we'll figure something out…" Leo said after a moment. "But if we can't-"

He was interrupted by a shrill shout echoing through the tunnels.

"Dudes, Bros… Anyone!? HELP!"

Leo broke into a run, trying to follow the yells. "That sounds like Mikey!" He gasped, putting on speed. To his relief, Raph was running beside him. Leo shot him a curious glance, and he shrugged.

"I ain't got anyone else to help me."

Leo nodded, turning to the left to follow the noises. He skidded to a stop, Raphael bumping into him and nearly sending him toppling. He had nearly run right off the edge of a platform into muddy water that seemed too far down to be safe. If he had fallen, it probably would've hurt like hitting concrete- if he would've even survived.

He scanned the area quickly, blue eyes spotting a squirming green spot clinging to a collapsing rusted ledge.

Mikey, Leo realized with a start. He had changed into a turtle too.

"Hold on!" He called over, backing up for a running start. If he was careful, he could just jump up next to him.

"Leo?" Mikey asked hopefully. "That you, dude?"

He broke into a sprint, kicking off the platform just as his toes met the edge. 'Come on, come on,' Leo thought urgently. 'Just let me make it!'

He landed on the ledge, quickly pulling Mikey to his feet just as a brace fell into the water. Only two beams were still supporting their weight, and they probably wouldn't last much longer. Leo turned to Mikey, looking into his wide blue eyes with urgency.

"Think you can hop over to that platform?" He asked, and Michelangelo nodded. "Then go!" Leo said, leaping across just as the last bolts came undone. Leo landed safely on the other side, but Mikey was not as fortunate.

He had jumped a moment too late, and his fingers just brushed the secure protrusion before he slipped, falling with a scream towards the filthy liquid below.

An emerald hand snapped out, snagging his wrist just before he tumbled out of reach. Looking down, Mikey saw the platform he had been standing on hit the water with an angry splash, and relief washed over him. He glanced up, smiling at his rescuer who was pulling him onto the ledge with a grunt of effort.

"I gotcha!" Raph said, hauling him up.

As soon as his feet were on the ground, Mikey shot up and pulled Raph into a tight hug, smiling widely.

"Dude… you saved me!" He squeezed just a little too tightly, and Raph nearly choked, struggling out of his firm grip.

"Alright, alright, I get it kid! Sheesh!" He grumbled, though Leo could see a ghost of a smile on his face.

"You…" Mikey sniffed, grinning up at him with watery blue eyes. "You're my hero!" He reached into the pocket of his sweat pants, yanking out a soggy wad of colorful paper. "I want you to have this back, as a reward!" He handed the paper to Raph, who took it with a look of confusion.

"Dis is…" His eyes lit up with a fury, and Leo stepped backwards fearfully. "You little rat! I knew you stole my comic book!" He grabbed Mikey by his hoodie front, practically on fire with rage. Mikey didn't seem to get that he should be scared for his life.

"Hey, man, it's still in mint-er, near-mint condition!"

"So that's what you stole!" Leo said, fixing Mikey with a disappointed stare. "And I stood up for you!"

Mikey snickered, dancing out of Raph's grip. "Hey I gave it back, didn't I? And besides, I don't need comic books anymore! Look at me now! I can be a superhero! Just call me, uh… Turtle Titan!"

Leo held Raph back from charging at Mikey and shot him a look. "Mikey, we don't even know if we'll stay like this or not. Right now, we need to find a way out."

"Aww…" Mikey groaned, deflating a little. "Leo, you're no fun…"

"Now's not the time for fun," Leo scolded as he turned back into the tunnel they came out of. "We need to find Donnie. If the three of us got mixed into this, chances are that Donnie did too."

"How do we know Don hasn't already found his way out yet?" Raph asked, glaring at Mikey over Leo's shoulder.

"'Cause Don-Don's probably trying to figure out how we changed." Mikey answered as he skipped alongside Leo. Leo and Raph halted, looking at the freckled turtle with a look of startled realization. They shared a look, and Mikey paused, wondering if he said something wrong.

"Uh, Mikey," Leo asked curiously. "Why would Donnie be looking for what changed us? Wouldn't he be more focused with, I don't know, getting out?"

Mikey shifted innocently. "Donnie liked using big words, and he was all mister-smart-guy, so I just figured… Did I say something wrong?"

"Actually, you might be right on de mark with dat one." Raph said, stunned, and Mikey beamed. "But don't dink dat 'cause you can come up with a good idea means yer off the hook for ruining my comic book!"

"Didn't think so, bro."

Leo paused, inspecting the water the tunnels were transporting. They stood back in what Leo assumed was the central pipeline, where he and Raph had been following upstream. "We floated downstream, right? That means we fell in the water further up…"

"So Donnie's headed there, too."

Leo nodded. "Let's go."

..::-::..

Honestly, Leo was amazed Raph and Mikey didn't harass one another in more than just insults. Raph seemed to get that Mikey was just goofing off, and his habit of smacking the smaller turtle became more of a teasing action than a spiteful one. Of course, Leo still had to step in when one got too harsh for the other.

They had been walking for almost twenty minutes when Leo began to notice the difference in the water. Thin, flimsy strands of iridescent aqua flicked through the stream, and the further they went the more there was. Leo suddenly stopped at the entrance to another pipeline. This was where that glowing stuff was coming from, and judging by how thick it was here, the source was just through that tunnel.

Leo looked over his shoulder. "Stay on the pathway guys. If this is the gunk that turned us green, who knows what more of it would do to us."

They nodded, although Leo didn't trust that glimmer of mischievousness in Mikey's eyes.

It was really a short tunnel, but what was at the end of it made Leo gape in shock.

"Whoooaahhh…"

They stepped out onto an island of spongy moss, incredibly soft and bouncy beneath their feet. A turquoise tree grew in the middle of the space, shedding shimmery leaves into a little lake of aqua-black liquid. Up above, where the ceiling would have been, was a crumbled hole that looked like it led into a subway station.

"So that's where we fell…" Leo muttered.

"Hey, guys!"

The trio turned when they were met with Donnie's voice, and they saw him running out from behind the odd tree. He fell victim to the transformation, too, it seemed. He still had his lanky height, but Leo could see flecks of red in his brown eyes that didn't exist before. He stopped before the group, studying them with a scientist's gaze, and Leo saw a gap between his two front teeth that he hadn't noticed until now.

"Fascinating…" The olive turtle mumbled. "I thought I couldn't be the only one affected, but the fact that our changes are so… so similar, it's astounding in and of itself! The chances of this happening are probably, like-"

"Will you shut up?" Raph grunted, obviously not liking being looked at as though under a microscope.

"Be nice, Raph." Leo chided. He turned back to Donatello. "I'm guessing you figured out what this stuff is?"

He shook his head, eyes glazed over as he ran equations and possibilities through his mind. "Not even close. All I've figured out is that that's the stuff that changed us. I think it's some sort of mutagenic fluid, but it doesn't even look like it's composed of earthly elements! It's almost like its alien!"

Mikey perked up. "Alien!? Cool! Like, are we talking about slimy monsters with robot bodies and laser guns that are here to take over the earth and have converted us to make us weapons or-"

"Not that kind of alien!" Donnie interrupted. "What I mean is, it could be some form of bonding agent to combine genetic building blocks into a new hybrid species. It may have come from alien origins, outer space, even, but I seriously doubt it has anything to do with actual aliens."

Mikey looked dazed, and Leo guessed he was still stuck on "bonding agent". "Jeez, Donnie, didja kill off his few brain cells or somethin'?" Raph asked, poking Mikey in the head.

"Huh? Oh, he'll be fine," Donnie said absently, scratching his head. "I'm just wondering how we discovered this and no one else has. I mean, wouldn't someone else have found this pool sooner? Things just aren't adding up…"

"Perhaps that is because it is not meant to make sense, but to defy it."

The four boys turned in surprise to see a figure step through the pipeline, tall and imposing. It wore a maroon robe that dusted against the little island's grass, and a tail swept out behind it. They gaped up at the biggest and most humanoid rodent they had ever seen.

"Perhaps an explanation would ease your minds. My name is Splinter."