"So what about you, huh?" Raphael asked. "How'd you get here, Karai?"

Karai shifted uncomfortably. "It's a long story," she said. "So get comfortable, because I'm going to tell it."

"For me, it started when the Foot Clan's grunts became ill. I had my suspicions - the flu? Pneumonia? Vaccinations aren't always totally reliable, you get some stragglers, some viruses that evolve to become resistant. I decided not to worry myself with it. Until my father or I started getting sick, it was really none of my business. We always had more than enough ninja.

"Then Father was sick, with the same thing that had been spreading through the rest of the clan. I figured it was contagious, but then, why hadn't I gotten sick? Or Bradford, or Xever? Dumb luck, maybe? I thought at first that it was something in the water, he would get better. But no one was getting better. People were dying, and in the most horrific ways. One new recruit was vomiting blood and his body was rejecting water, of all things, and then he just... died. We figured it was dehydration.

"When I went to check on my father, the disease had ravaged his body. He... he hadn't been sick for a week. I remained by his side until he passed." She paused, her once-lively eyes taking on a sadder hue of yellow. "Normally death doesn't faze me. It happens, it happens. Nothing you can do to stop it."

Leonardo held his hand out to her. "We know how you feel, Karai. You're not alone."

She ignored his hand and continued her story. "About an hour later, he opened his eyes. But it wasn't him. What he'd become wasn't human, so I killed it. Drove a knife right through his head - it was easier than it should have been. His bones were rotting and his skull was no exception.

"So I decided to look into it, and try to figure out exactly what had killed my father and his clan. It was a while before I realized what it was, and why I hadn't met the same fate. I was right on my second guess that there was something in the water. And to be honest, I never liked the taste of tap water. It's an offense to the tastebuds. It still didn't explain why Xever and Bradford lived, but they'd decided to jump ship when the Shredder died."

"Actually," Donnie piped up. "We figured out why Dogpound and Fishface didn't get turned. It was... heh, it was all on accident, to tell you the truth. When Splinter, April, and us had to leave the Lair - an even longer story, don't ask - April was the only one out of all of us who got sick from drinking water. I figure it's because of the mutagen that we're resistant to the virus. Our immune systems are probably amplified because of it. Now - now I'm not saying to go mutate yourself! The last thing anyone needs is to get unstable alien substances all over their body, but..."

"Wait," Karai interrupted. "If you're so resistant to the virus, then where's your Sensei? Why did you have to amputate Michelangelo?" The turtles' expressions took on a mostly downcast look, and Karai felt a small pang of regret for asking that question.

Donatello continued. "My... my hypothesis is that there are two different strains of the virus. One that spreads through water, and one that spreads through biting or contact with infected fluids or tissue. The first strain is probably much weaker, and a mutant's immune system would be able to take care of it fairly quickly, unless it entered the bloodstream directly.

"Master Splinter... he got bit when we were ambushed. There was... there was nothing we could do for him, the way he'd been bitten. Mikey was bit earlier."

Karai's voice was as dry. "I'm sorry."

Casey Jones didn't know what time it was when he woke up.

He didn't know /where/ he was, either. The immediate area was clean, but dull - clearly spring cleaning wasn't a priority here - and several gadgets he didn't understand were within his sight. For the most part, though, the room was barren, save for the couch he'd crashed on and some chairs strewn across the room, like an impromptu living room. He vaguely remembered coming here with that one girl who'd introduced herself as Karai, and the kid... crap, what was her name again? Aubrey? Audrey? It's too early in the morning for this, he thought.

Was it even morning? He couldn't tell. He yawned, stretched, and rubbed the sides of his head before finally standing. Casey twisted his back sharply, cracking his knuckles and forcing the sleep out of his bones. Looking around as he tilted his head from side to side, cracking his neck and groaning, Casey's eyes locked on a bottle of water across the room. "Might as well," he said aloud to himself, noting the dryness of his mouth and figuring it couldn't hurt. He grabbed the bottle off the floor where it sat, right by the leg of a chair, uncapped it - the bottle was a bit less than half-empty - and had just taken a gulp when he heard a boyish voice from across the room snicker and say, "I backwash."

Casey spewed the water from his mouth, spraying the immediate area and the furniture, along with the turtle leaning over the back of the chair. Mikey jumped up and moved his arm-stump out of the way to avoid the spray of water, remembering that Donnie told him to be careful of getting the bandages wet. Warm water from the boy's mouth hit him over the face and Mikey laughed as he wiped it from his face. "What the hell?!" Casey shouted.

"Oh man!" Mikey exclaimed through his laughter. "You should've seen your face, dude!"

"Ass," Casey grumbled, taking a short sip anyways and pausing right before he swallowed. "Wait." He spun around, almost comically, pointing at Michelangelo and sputtering, "What the fuck?! What is th- what are y- holy shit-" He was silent for a moment afterward, getting his thoughts in order. "...Turtle?"

"No duh, dude. Can't you see my totally kickin' shell?" Mikey turned around, pointing back at it with his functional and existing fingers.

It felt like forever with Casey standing there, dumbfounded, before shaking his head and saying, "Eh, I've seen weirder. Y'know, all these zombies walking around?" He laughed uncomfortably. "So, have you always..." he paused, making vague hand gestures toward Mikey. "Have you always been like... like this?"

"What, a turtle? Yeah, I've always been a turtle!"

"No! No, I mean like... a big turtle. Turtles don't usually look like you?"

"Oh yeah, I got hit with a slime ball when I was just a baby, by the evil doctor Boiled Beets!" He raised his arms and voice on the last part in an attempt to scare Casey, looking over at the stump of his left arm and wiggling it as he grinned. Casey stared at the turtle with wide eyes and blinked a couple times, shaking his head and clearing his throat.

"Alright, well, uhm... alright." He cleared his throat again and bent down to pick up the bottle of water, tapping the side of it before looking up to the turtle.

"What's your name?"

"Mikey!" He thrust out his hand. "And I'm just joshin' with you, dude. We're cool."

"Well, it was," he laughed and took a few steps back. "It was really great meeting you, yeah but, I have to go now and find the little squirt we brought with us, so... I'll see you later?" His statement came out more as a question. A question that he had no intention on waiting for an answer to as he turned on his heel, making his way out of the room and into the first one on his right.

The room he had entered was definitely familiar with cleaning supplies as its walls and floors were spotless and it smelled of disinfectant. There were gadgets here as well, but these ones Casey could identify as medical equipments. Another turtle, this one taller and leaner than the one he had talked to outside, was busy mopping up a pool of blood on the side of a medical slab.

He stumbled over a stray tube that was laying out from a box, cursing softly and Donatello looked up at him, a tooth-gapped grin spreading across his face. Finishing up the mopping and placing it back into the bucket of now pink water, Donatello walked forward to meet Casey with an outstretched hand. Casey took the offered hand and shook it with his own grin, already getting used to the fact that his hosts were turtles. "So," he drawled with a grin. "Turtles, huh?"

"Mutant turtles, to be exact," Donatello pointed out and let his hand slip from Casey's. "Donatello."

"Casey." The purple-masked ninja watched the boy as he craned his neck up and around to look at all the different equipment around him, all medical and sciences that Donatello was sure he had never seen half of before now. He cleared his throat and Casey looked up with an arched eyebrow, which Donatello took as a sign to go ahead.

"I didn't want to ask earlier, seeing as you were already asleep by the time I came out but, I'm going to have to perform an examination."

"Examination?" Casey asked, surprised at the order, then a grin spread over his face and he winked. "Aren't you gonna take me out for a date first?" Donatello sputtered for a moment before he simply huffed, a deadpan expression falling over his face and he simply pointed to the table, watching as Casey lazily boosted himself onto the table and made his way over.

Laying back on the slab, Casey watched the tall mutant grab a few things off a equipment tray - something that looked like a scanner and a few needles - and then turn to him. The other one, Mikey, hadn't been very much help and Casey wondered if this one could give him more to go on with the whole 'giant, mutant turtle' thing. "So, your other turtle friend isn't much help, so I'm gonna try a crack at you for an answer," Casey lifted his arm as instructed and watched the scanner go over his skin in trance at the green light, before shaking himself out of it. "How are you turtles?"

"How are you human?"

"Let me try again," Casey cleared his throat a few times, smacking his lips once or twice before asking again. "How are you all talking and walking and looking like a person?" Donatello hummed at Casey's question, continuing his thorough scanning of the boy's body and made sure to double check each reading as he went, answering as he did so.

"It's a long story, but to make it shorter I'll just explain what made us - for lack of a better word - mutate into how you see us now." Donatello gestured for Casey to sit up and tied a rubber rope around his arm, tightening it around just below a bicep and tapping over the veins in Casey's elbow. "Flex, good, keep doing that - The substance that made us like this is called mutagen, a transformative compound from another dimension that was brought here from there."
Casey hissed as Donatello slid a needle into the popped out vein, watching as the turtle pulled back on the syringe and it began to fill with blood. A little under half the syringe's holding capacity was taken before Donatello slid the needle out, putting the pad of his finger against the needle gently with a cotton pad. He pressed down quickly once the needle was safely extracted and placed it in a holder as he grabbed a bandage, fixing it over the cotton pad and untying the rubber rope. "It changes whatever it comes into contact with, splicing its DNA with the last organism it has been in contact with. For example, the last thing that my brothers and I had been in contact with was a human before we were touched by the mutagen, hence why we are so similar in appearance to you, while still maintaining the more obvious characteristics of a turtle."

Donatello took the syringe and pushed down, squirting a small puddle of blood over a microscope slide and pressing the two glass slides together. "However, mutagen is so unpredicatable that one can never know for sure how it will react," he said as he squinted into the microscope, fiddling with the focus and bringing them into clarity. He couldn't find anything abnormal right away, but the purple-masked turtle would rather be safe than sorry and looked over every milimeter critically. "Another example for you is with a friend of mine who had not been in contact with another organism recently before his contact with the mutagen and, essentially, was turned into a giant ball of slime. I'm not sure the time period in which someone has to be in contact with something beforehand to have an affect in the mutation, but seeing as what we're dealing with now, we don't really have the time or luxury to experiment."

Casey listened to Donatello explain the mutagen, drinking in the information and for once finding science interesting. His interest peaked higher at the mention of brothers and it clicked in his mind that Mikey must have been one of them. "Brothers?" he asked. "Mikey, right? Who else?"

"I have two other brothers, Raph and Leo. Leo's the oldest, then Raph, then me and Mikey."

"Middle child, huh?"

"We're an even number," Donatello said dryly. "There is no middle." Casey scrunched up his face, mouthing Donatello's words in a mocking manner and crossed his arms, wincing at the soreness that was already travelling down his arm from the needle. He looked up when Donatello got up and drew the slide of Casey's blood out from underneath the microscope and the boy grinned up at him. "So, what's the verdict, Doc?" he asked. "Am I gonna live?"

"I didn't find anything strange in your blood, so if you keep the walkers off you," Donatello nodded. "You're fine." He bent down to grab a juicebox from underneath the equipment cart, placing it in Casey's hand and pointed down to it once he had pulled away. "Drink that and sit for a few minutes to let your body make up for the blood I took," he said, and walked back around to the slab where Mikey had been before, taking a rag and starting to wipe the blood off from the slab. He saw Casey eyeing it and he shifted uncomfortably, cleaning off the drying blood in small circles to deep clean the stains before sighing softly.
"Mikey got bit," he said in a dull voice, shrugging hopelessly. "Had to amputate or he'd be out there stumbling through the streets like everyone else."
"That must have sucked, having to cut off your own brothers arm."

"Yeah..." Donatello stopped cleaning for a moment to stare down at the table before shaking his head and continuing. "Yeah, it did."

"Seems like he's already getting used to it," Casey laughed and sucked on the straw, scrunching up his nose at the cool room tempature juice that ran down his throat. "He just started flicking his stump around and grinning at it."

Donatello laughed, "Yeah, sounds like Mikey." The two fell into silence, the quiet slurp of a straw and the smooth sounds of a rag being drawn in circles over the table where all that was heard, until Casey made a curious noise and Donatello looked up. He paused in his work, brow raised and Casey stifled a laugh. "You said that mutagen splices your DNA with whatever you touched last, right?"
"The last organism another is in contact with, yes... why?"

"What if the last thing you touched was a zombie?" Donatello stared at Casey for a long time before putting his rag down and crossing his arms, bringing one hand up to stroke his chin and scratch his jaw. His thoughts were going a mile a minute and the question had opened doors that he hadn't even put a thought to. Lower lip jutting out as he thought, humming in his thought, Donatello finally looked up at Casey. "From a scientific standpoint, I would think the organism would simply gain a zombie's unlimited endurance and not need as much nutritions as those who are not infected." He chewed on the inside of his cheek before continuing. "Seeing as how the organism was never bitten - therefore, the virus never be transmitted - they could very easily become cannibalistic, but without the ravenous hunger our undead friends possess."

"So they wouldn't be dangerous?"

"It depends," Donatello said, his tone taking on one that meant his victim - as Raph liked to put it - was in for an explanation. "If a human were to be in contact with a zombie before contact with mutagen, they would most likely gain the abilities and hinderence I stated before, and probably retain their mentality - hopefully. However, another organism such as a dog or cat, could very well lose themselves and become just like a zombie, but would not have a lethal bite as they were never in contact with the virus itself - only the mutagen."

"So... they are a little dangerous?"

"It all depends on circumstance, I would think."

"And if someone or something is bitten by a zombie before getting mutagen dumped on them?"

"We'd be faced with a mutant zombie, simple as that." The turtle picked up the rag and started cleaning again. "When mutagen is added to something already mutated it becomes far more powerful and farther into the mutation, and, I would assume for a zombie, it would become harder to kill - and with heightened senses." Casey nodded slowly and stared at Donatello, imagining the turtle suddenly as an unstoppable zombie and he leaned back a bit as he brought his juicebox to his lips and closed around the straw. A sudden thought came to the boy's head and he gulped down the juice, setting the empty carton aside and looking at Donatello.

"So, if Mikey had..."

"We would have either had to kill him before he turned or after, when he would most likely kill half of us in the process," Donatello said, his voice now tired as he thought of what could have happened and he shook his head. "I'm just glad he got back here in time, before the virus spread... If he hadn't, I would have killed him myself."

"You would have just... done that?" Casey asked quietly with wide eyes, shocked that a brother would do that. Donatello snapped his head up. "Kill your brother? Just like that?"

Donatello slapped the rag down on the table with a sharp slap, making Casey stiffen and eye the bo staff strapped to Donatello's back. "I wouldn't have enjoyed it," Donatello hissed with a voice that dripped venom, his eyes narrowed into dangerous slits. "But I'd rather have him die as himself, than die as one of those things!"

"Hey, calm down!" Casey said and put his hands up in surrender. "I'm sorry, I shouldn't have said anything!"

"No, you shouldn't have!" Donatello hissed in the same voice and glared across at the teen. "Don't sit there and ask me how I could do such a thing when you don't know anything. I've already lost my father to the virus, ripped to shreds by the reanimated, and I will /not/ let my baby brother be turned into the very thing that left this family in shambles!"
"Don-"

"I won't stand by and watch my family tear each other apart!" Casey hung his head, ashamed at what he had said and implied towards the turtle, fiddling with the straw of his juicebox and squeezing the tip. Donatello's breaths came in angry huffs and he went back to messily cleaning, slowly calming down as he cleaned in the small circles and he let out a sigh. "If the little girl you brought here, Aubrey, were to suddenly become infected," he said softly. "Would you sit and watch her turn?"

Casey thought for a moment, his eyebrows narrowed as he clenched and unclenched his jaw, although it took no real thought on his part as he thought of the young girl's bright smile. "No," he said finally in a quiet voice. "I wouldn't."

"Neither would I." The two fell into a silence once again and when Donatello had finished cleaning the slab, he told Casey he could leave the medical area and go explore, giving him a friendly pat on the back to reassure him that there were no hard feelings. When the teen had left and the turtle was alone in the room once again, Donatello turned around to lean on the slab and he covered his face with his hands. Holding back a sob and wail, he uncovered his face and tilted his head back as he blinked rapidly to rid himself of the tears that threatened to slide down his face.

If things had turned out differently, and he would have had to kill his own brother - his baby brother - that would have left a stain on him that no amount of scrubbing would get clean. A piece of his heart, his life, would have been ripped away because of him and he inhaled sharply with a shake of his head as he got back to work.

A/N: This one was long overdue and for that I'm sorry! We should be updating regularly once Chess catches up with the series!