Lucky ducks ... I know I didn't give you much in the last chapter so here, have another.

The moment she opened her eyes, Leo pounced.

She was already lunging for Splinter, halfway up and across the table, when he threw his arms around her to yank her back. She bit him.

Her fangs burrowed and locked onto his forearm, spearing him with a pain that shot up to his shoulder and drew a yelp from his throat.

A chorus of voices shouted his name, a couple shouted at Karai, and then there were hands on them both.

His sensei, who for a moment had intuitively taken a leap back from the threat, was now somehow both gently and forcefully trying to pry Karai's jaw apart saying, "No, my daughter, we are not your enemies! Release him."

Mikey and April were trying to hold her down as her body thrashed and writhed, trembling as though it wanted to shift back into its serpent form but didn't. Casey had taken a step back and was staring with wide eyes. And Leo was pretty sure the arms encasing him now were Raph's, ready to pull him away the moment Karai's teeth were removed. He was also the stronghold keeping Leo on his feet, though the older turtle wasn't sure if Raph actually knew how close he was to fainting.

A stream of raw heat slithered through his veins, slowly crawling its way up his arm as though there were microscopic mutant parasites scuttling beneath his skin. His stomach lurched with an intense wave of nausea. He found himself opening his mouth and nearly puking out Donnie's name. His knees quaked, and the cluster of chaos surrounding him went out of focus. He felt Raph's brawny arm lock more firmly around his torso.

His purple-banded brother responded by rushing forward with something in his hand and turning his back to Leo who just caught a glint of silver as Donnie made a swift stab toward Karai. Only a few seconds passed, during which Leo was sure he'd hurl all over Raphael, before he could feel every centimeter of Karai's fangs drawing out of his arm and then the gush of blood that followed it.

He and Raph stumbled backward with the release, and when he blinked next he was on the ground, shivering in his brother's embrace and breathing shortly.

He was vaguely aware of Raph's short-tempered voice shouting at people, and then of Donnie appearing with beads of sweat rolling down his forehead as he yanked off Leo's mask and tied it so tightly around his bicep that his fingers immediately went cold and he could hear himself groaning. The pain that had been rippling through his body now seemed intensely confined to his left arm and it throbbed with a hot ferocity that made him quiver and blink slowly and caused his stomach to heave again. He wasn't sure if anything came out of him, but he guessed it must have because Raph suddenly forced him on his side.

When his stomach stopped convulsing, he let his cheek fall against Raph's arm, grateful for the coolness of his brother's skin. He couldn't hear what anyone was saying, yet it seemed the whole room had erupted with pandemonium. But it soon seemed not to matter as he glanced up to where Karai was laying, miles away it seemed, and his eyes slid close.

When he blinked himself awake, for a few seconds everything was a blur. His stomach was as dense as a rock, and his left arm felt just as heavy, so much so, in fact, that he was surprised it hadn't fallen through whatever he was lying on. The lab table, he decided after closing his eyes and noting the flatness of the surface and the way it neither conformed to his body nor his temperature. It was cold and smooth and hard beneath him, like a block of ice that wouldn't melt. He was lying on his side with a pillow beneath his head and his left arm stretched out in front of him, wrapped tightly in a coil of gauze. Essentially he was glad, lying on his shell on hard surfaces normally didn't amount to very much comfort, and this way he felt like he didn't have to move himself too quickly.

"Leo?"

Warm, slender fingers stroked his cheek and he opened his eyes again, this time letting his gaze focus on the red-headed girl crouching in front of him.

April smiled when he was looking directly at her, and she shook her head. "Leonardo, you are the luckiest turtle on the face of this planet," she said with a laugh.

He didn't see what was funny, especially since his head was too full to process what had just happened.

But his brother's voice cut off his attempt at trying to remember. "He awake?"

April looked over Leo's shoulder and nodded. He heard the sound of stool legs scraping against the cement and soon Raphael came into focus. One of his rough hands rested itself on his shoulder with a surprising amount of gentleness, and Raph's bright green eyes peered down at him as though assessing whether or not Leo was fully conscious. When Leonardo neither spoke nor blinked, Raph scoffed under his breath - a release of air that sounded unusually relieved - and the red-banded turtle punched his shoulder.

"Jackass," Raph said under his breath, a grin hiding in the corner of his mouth. "How many times d'you gotta pass out before you realize being heroic has consequences? This ain't a TV show, bro."

"What happened?" Leo mumbled.

This was when Donnie appeared, nearly shoving Raph out of the way in his hurry to answer the question. He was rubbing his hands with a cloth, skin frighteningly pale and glossy, but smiling like he'd just made the discovery of the century.

"Leo, either you're an absolute genius or this is the greatest ray of serendipity since the discovery of penicillin!"

"What are you talking about, Donnie?" Leo groaned, beginning to close his eyes again.

In his moment of temporary blindness, he heard Raph growl something and probably push Donnie to the side, which would've been the reason why Donatello stumbled against the edge of the table and why April said something about Raph holding his temper for five minutes.

Leo allowed himself to rest durning this exchange, taking an odd bit of comfort from the argument that followed, and all too soon someone was shaking his shoulder and he opened his eyes to Donatello this time, who was now sitting directly before him, still smiling.

He looked exhausted, and Leo immediately worried. Donnie knew he wasn't supposed to be straining himself, yet he looked nearly as terrible as he had in the days preceding his bout of septic shock. If it wasn't for the light of excitement glittering in his eyes, Leo might've found his condition alarming enough to switch places with him.

"Donnie, how long have you been awake?"

"Something happened during Karai's mutation," Donnie said in that quick, breathless and enthusiastic tone he got when he was talking about science. He completely disregarded Leo's question.

"My hypothesis is that Stockman mixed a small dose of a faulty retro-mutagen compound into the mutagen that he had already infused with serpent DNA. It had to have been accidental, because I don't think that the Shredder would have wanted his mutant to phase between a human and mutant form, knowing that he'd never intended to mutate Karai in the first place. This little fluke is what allowed Karai to change in between forms."

Leo furrowed his brow. "What does this have to do with me?"

Donnie's smile widened. "You were the one that discovered this, Leo! Or well, technically I did, but if you hadn't jumped between Splinter and Karai and gotten bitten then I would've tried the retro-mutagen I'd made weeks ago on her and it would've failed!"

Leo blinked and immediately began to push himself up. His arms trembled under his weight. Donnie took hold of his good arm and pulled him into a sitting position before hopping up next to him on the table. They were the only two in the lab now, though the door was open and he could hear Raph and April talking just outside it.

The older turtle looked back to his brother who hadn't yet lost his enthusiasm. "Are you saying the retro-mutagen you made won't work on Karai?"

He didn't understand why this made Donnie's smile stretch. "It wouldn't have worked," he said pointedly, holding up at finger. "But when you got bit, Karai injected you with her venom. I was able to tie off the circulation in your arm before it could spread to the rest of your body, but I had to get it out of your system somehow or I would've had to chop your arm off!"

Leo blinked a few times, leaning a little away from his brother who was still grinning like this was the best day of his life.

Donnie waved a hand. "Long story short, I was able to extract all the venom from your blood and I decided to study it for good measure—and I'm glad I did because I was able to break down its components and figure out how she was able to transform back and forth from human to mutant."

He hopped down from the table in a sprightly kind of way and walked over to the adjoining desk that was littered with beakers and vials and papers of notes next to his computer. He shuffled around for a specific sheet of paper and held it up for Leo to see, but all the older turtle perceived was a confused mass of random letters, numbers and equations.

"I was able to take the genetic makeup of Karai's specific mutation and reconfigure her DNA to modify the retro-mutagen I'd already made!"

Leo blinked again, not sure if he was completely lost or if his brain was just taking a while to catch up. "So …" he said slowly. "You changed her back?"

This was when Donnie's smile faltered. The paper in his hand found its way back on the table and was replaced by a small vial of bright blue liquid. "Not yet," he said, gazing at the new retro-mutagen for a moment before smiling softly at Leo again. "You woke up just in time though. I just finished testing it on a sample of Karai's current strain of DNA. It works. We just haven't used it on her yet."

Leo furrowed his brow, still feeling intensely sluggish. "How long did all of this take you?"

"Not long at all. Hardly a week!"

Leo's heart skipped. "A week! I've been out for that long again?"

Donnie bit his lip but there was no containing the laughter that escaped from his nose. "I'm sorry," he said with a delirious giggle. "I just wanted to see your face."

He cleared his throat. "Hardly, Leo. It was a joke. It's only been about fifteen hours and you've been waking up at least every three hours and seventeen minutes to vomit." He shrugged. "Side effect of the venom, I suppose."

Leo stared, allowing his pulse to calm and withdraw the heat from his cheeks, then he lowered his eyes to his feet hanging over the cement floor. His fingers curled around the edge of the table on either side of his hips. Then he thought of something that made his head pop up again.

"If you haven't changed her back then where is she?" he asked, jumping to his feet before he realized he was doing so. Donnie rushed over and helped him steady himself before he could stumble and fall on his face.

"Take it easy, Leo. Your muscles have to readjust to moving around."

Leo clutched his head to ward off the dizziness for a moment and then held up a hand to signal his brother that he was fine. Once he'd regained his balance, he looked back at Donnie.

"What did you do with her?"

At this Donatello finally looked appropriately less animated. His eyes shifted before he glanced back at Leo. "I'll take you to her," he said then gave his brow a pleading furrow, and stared Leo down with those large brown eyes of his. "But you have to let me give you a look over first. The side effects of mutant venom could be just as unpredictable as mutagen itself."

Leo sighed, softening quickly under that doe-eyed gaze. He pulled himself back up on the table. "Fine, but be quick about it."

Donnie's smile this time was as delicate as an abandoned feather. He took Leo's wrist in his hand, pressing his thumb firmly against his veins and counted beneath his breath. Then he checked his reflexes, searched his eyes with a flashlight, took his temperature, and asked him a number of questions that Leo recited the answers to like he was a contestant in a spelling bee.

The blue-banded turtle hated check-ups as much as the next person, but he would've been lying to himself if he denied that there was a certain appeal to Donnie's meticulous nursing disposition. Though, it was an appeal coated with irony when Donatello paused to keep himself upright and focused, squeezing his eyes shut and drawing in a long breath before returning to fuss over Leo.

The older turtle knew this pause all too well by now and wondered when this cycle would end. Being ninjas, he and his brothers were always procuring injuries—occasionally illnesses—but lately it seemed that Leo and Donnie had both drawn one end of the shortest straw in the bunch and were left to cling to one another in infirmities. Leo swore he could feel Donnie's exhaustion in the marrow of his own skeleton.

"Your blood pressure is a little low and it doesn't take a genius to guess that you're blood sugar is probably lacking too. But this is to be expected. Eat something, drink some juice, don't move around too much for the next twenty-four hours. You won't die."

Leo smiled. "Thanks, doc … And how are you?"

"Hm?"

Leo cocked his head. He said nothing and he knew his brother was aware of the message he was trying to convey. But Donnie simply stowed his medical supplies away and started for the door.

"I'll take you to Karai now."

Leo sighed internally and slid off the table to follow him out. April and Raph were still standing just outside the door, no longer talking now, and they both straightened their backs as Leo and Donnie emerged.

"He wants to see her," Donnie said to April's quizzical look, and her expression took upon just as much discomfort as Donnie's had when Leo had asked where they were keeping the new mutant. This made his stomach turn, and rendered him less aware of the look Raph had fixed him with.

The four of them crossed the lair, Donnie in the lead. And Leo said nothing as he was guided past the turnstiles and they all headed through the scape of tunnels, though he did become instantly anxious. He trusted his family to take care of Karai—especially Splinter—but in her state, he knew there was little they could do that would be comfortable for everybody. He wondered what they'd done with her, how they were keeping her from escaping, how they were keeping her nourished, though this part made him shudder. He had no doubts as to what Karai's diet most likely consisted of now and he didn't want to think about it.

He nearly got lost in the twists and turns they took throughout the tunnels even with as much experience as he had traversing the very same maze. It took a long time, during which the four of them hardly spoke and he was starting to notice Raph's gaze adhering to the side of his face, though every time he glanced back, those green eyes were carefully staring off to the side. Leo said nothing about this either and allowed Donnie to finally lead them to a small alcove that was barred off at the entrance they walked up to.

There was warm yellow light filling up the archway, and the first thing Leo noticed was his sensei kneeling close to the left-hand wall, eyes closed, hands on his knees, though Leo could tell he was not so much meditating as he was waiting and trying not to acknowledge the sounds that echoed under the domed ceiling. Mikey and Casey were sitting by the opposite wall. Casey had his back slouched with his shoulders against the wall and his hood over his head, playing a game on his phone that partly contributed to the noisiness of the tunnel. Mikey was leaning over his shoulder, watching, a lumpy cloth bag sitting on his opposite side.

Rats, Leo informed himself with a twist to his stomach.

The little turtle in orange looked up as the four of them approached and he immediately popped up with a bright smile. "Leo!" he exclaimed, nearly knocking his older brother over as he ran up and threw his arms around him.

Raph had pried him off and shoved him to the side within the next second, but Mikey seemed unfazed by this.

"You're okay," he said, beaming up at his leader.

Splinter was standing by now and walked over to rest a hand on Leo's shoulder, a faint but real smile concealed beneath his fur. "It is good to see you on your feet, my son."

Leo blinked at the indecipherable flash of emotion that had just crossed his sensei's eyes. "It's—good to see you too, Sensei."

"Please tell me you've got that retro-mutagen figured out now, Don," Casey said, pushing himself to his feet and pocketing his phone. "If I've got to even look at another rat, I swear I'm gonna hurl. No offense, Splinter," he added quickly, his eyes flashing to the giant rat in the tunnel.

Splinter nodded his head forgivingly. "I understand your discomfort, Mr. Jones."

Leo glanced toward the bars in the archway as the other noise he'd been hearing grew closer and more alarming. He jumped back and stumbled into Raph as Karai's serpent form slammed into the bars and then writhed quickly back into the shadows, her vicious hiss still thick in the air.

Leo frowned and found himself breaking away from the group as his feet carried him closer to the archway. His fingers curled around the bars and he pressed his face against them to peer into the space beyond.

It was a small and empty chamber with two other outlets, both of which had been sealed off. The ceiling was high and there was very little light save the lantern on the floor near his feet that cast a bar of golden light across the floor of the chamber. Flashes of white streaked by once and then twice, and it took him a moment to realize what she was doing.

She was trying to find a way out—an escape—throwing herself against the walls, slithering from one end to the other and back. Her hisses and shrieks were venomous and full of raw anger, and somehow he knew she hadn't stopped doing this since she'd been put there … She was a caged animal.

His shoulders dropped and he felt an ache of guilt in his gut as he continued to watch her, knowing that he was part of the reason she'd been locked up.

He felt a hand on his left shoulder and looked up at his sensei who was staring through the bars as well. There was a glint to his eyes that told Leo he felt the same way.

"She will not be here much longer," the old rat said quietly.

Leo nodded once, looked back at Karai, and then turned to his brother in purple. "How fast can we get this done, Donnie?"