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Donnie ran through the sewers, hurriedly pushing the manhole cover out of his way. As soon as he was in daylight, he aimed for invisibility, running into an empty alley.
Donatello scaled up the side of a building, using window ledges and fire escapes for leverage, and he made his way to the Foot Headquarters.
The tall skyscraper seemed quiet when he approached it. Nobody walked in or out of the large double-doors. No cars stopped to park in the small lot on the side.
The air held a sort of rigidity, as if everything at that very moment was permanent, and Donatello shuddered as he raised his eyes toward the cloud-covered sun.
The lone turtle took a deep breath and gulped, wondering if his brothers would be in the same room as last time, or if they had moved them.
He waited in the shadows of the trees, his arms crossed over his chest.
Suddenly, there were footsteps behind him, and in a flash, he'd pulled out his bo staff and readied himself for a fight.
"Woah, woah, woah, cool it," came a familiar voice. "It's jus' me."
"Casey," Donnie sighed in relief, lowering his staff and straightening up. "Thanks for helping me with this. You didn't tell April, did you?"
"Nah, I just snuck out and told 'er I was gonna go get some milk," Casey replied, smugly.
"And... She believed that?" Donnie inquired doubtfully, raising an eyebrow.
"No," came April's voice from behind Casey. "She didn't believe that."
"April!" Casey turned around, guiltily. " Wha - what're you doin' here?"
"I could ask you two the same question," she replied. "What's going on? Where's the rest of the guys, and why are we at the Foot's Headquarters?"
"Uh-" Donnie sputtered, lost for words. "Look, April, I really can't tell you. This one- this one's too dangerous. I just need Casey as a distraction, and he's going right back home. This is something I need to do alone; you don't need to get involved."
"That's nonsense, Donnie," April replied. "You know we're in this together. Where's Leo, Mikey and Raph?"
Donatello hung his head and tried to make his breathing steadier. He was suddenly getting the crushing feeling that this was all his fault. It may or may not have been in reality, but Donnie had been trying to push everything to the back of his mind in denial.
His brothers weren't really captured by the Foot. They weren't possibly being dissected at that very moment. No, no, they were just gone temporarily.
Don only had to go and get them, and everything would be okay again.
His subconscious theory was getting a little shaky in the presence of Casey and April.
Donnie took a deep breath and put his hands on either side of his head, wondering if his whole world was coming crashing down around him.
"Look, they're in the Foot HQ somewhere. I have to go in and find them, and I can't do that unless Casey is the distraction. Please, April, go back home and Casey will be back in half an hour," Donnie tried to rationalize calmly.
April studied Donnie for a second.
"Something's wrong," she concluded. "I can tell, Donnie. You're acting strange."
"I'm not acting strange, April, alright? Please, just go home."
Donnie grabbed Casey by the arm and hurriedly tugged him toward the Foot building.
"Donnie!" April shouted behind them.
"Jus' go home, babe, I'll be back in half an hour," Casey replied as April disappeared from their view.
"Fine!" they heard her huff, and Donnie sighed in relief. It was bad enough that his brothers had been captured; he didn't want April being in on it, too.
"So, uh, they been captured, huh?" Casey asked, pulling his mask from his belt and sliding it onto his face.
"Yeah," Donnie replied. "I'm the last one. I HAVE to save them. Who knows how long we have until...?" Donnie trailed off.
"Ya sure ya don't want me to, ya know, stick around? Case somethin' goes wrong?" Casey asked.
"No, I have to do this alone. It's no use for you to put yourself in danger, too," Donnie answered. "I could never forgive myself if you and April got captured. Just... If I don't come back out, don't tell April what happened. She would only blame herself, and there's nothing she could've done, either."
Casey nodded silently, not really understanding, just knowing it meant a lot to the purple turtle.
The pair walked onto the sidewalk in front of the building. Casey pulled out his hockey stick and took a last look at his friend.
"Good luck, man," Casey said, giving him a punch on the shoulder.
"You, too," Donnie gulped as Casey turned to the entrance of the building and pushed the doors open.
Donatello took a second to wish none of this had happened before he jumped up above the door and landed on the window ledge just above it.
"-outside!" Don heard Casey yell inside. "You have to help me- There's turtles out there-"
A few seconds later, several Foot ninja and Purple Dragons ran outside, headed down the street, chasing the 'turtles' Casey had told them about.
Donnie waited. Casey should now be finding his way to the controls, so he could turn off the cameras and sensors.
It had been about ten minutes and Donatello was getting worried. He was prepared to go inside and find his friend when Casey came bursting out the front doors.
The long-haired man turned up to Donnie, gave him the thumbs-up sign, and yelled, "They're all yours!" before running down the street.
It was time.
He couldn't mess this up. Donnie turned to the window behind him and pushed it open. It led into a dark room on the second floor, and he waited a few seconds for his eyes to adjust.
The room was empty, so Donnie made his way to the door. He kicked it open and walked into the hall.
Empty.
The white lights above his head buzzed quietly, and Donnie's nerves felt about shot. He decided to go up to the twelfth floor, the last place he had seen his brothers.
Figuring the stairs would be more inconspicuous than the elevator, he ran to the end of the hall and practically sprinted up the ten stories.
Donnie's ribs were throbbing, and he knew if the ninja didn't kill him first, his injuries sure would.
He found the room Mikey had led him to the last time they had been in the building, and walked right into it.
Letting his eyes adjust to the dark, Donnie held his breath and crouched.
Empty.
Even the giant glass observation box had been moved. The window was still busted from where he'd fallen through it, and the turtle sadly left the room.
Back in the white light of the halls, he felt vulnerable. He had twelve floors to check now, if his brothers were even still in the building anymore.
He thought about how hopeless the situation seemed and felt a deflating feeling in his chest, like when he created a hypothesis on a theory he had worked so long on, and after several tests and experiments, it turned out his hypothesis was wrong.
Except this feeling was ten times worse.
Because if his theory was wrong this time, his whole family could die.
'Think,' Donnie told himself. 'If I were a Purple Dragon and I put the turtles on this floor, it must have been for a reason. The last place someone would check would be right next door. Right?'
Donnie walked to the room to the right and picked the lock.
The room was empty.
Agitated, Don went to the room to the left of the original and picked that lock, too. He didn't want to kick it open in case someone heard him.
He swung the door open and looked inside the room.
Empty.
With a sigh, Donnie walked to the room across the hall from the original door. If his brothers weren't in this one, he didn't know what he'd do.
He bent down to pick the lock, thinking that it was awfully quiet in the headquarters. Something was wrong.
That's when he saw the movement out of the corner of his eye.
Ninja.
Donnie jumped up, whipping out his bo staff and crouching into a defensive position.
It already seemed impossible, Donnie noted gloomily. There were dozens of them, filing out of the elevator.
How did they know he was here? Had they heard him? Was Casey okay? April and Splinter?
The ninja surrounded Donnie, and his mind cleared expect for one thought: fight.
"Yaaa!" Donnie screeched, diving into the ninja, his bo staff reverberating off the heads of several Foot.
He ducked and screamed and kicked, fighting like a madman.
Donnie thought of Leo, always wanting to conform, to follow the rules. His head pounded.
He thought of Raph, keeping so much inside of himself; the only emotion he felt safe to show was his anger. Donnie let his anger drive him against the ninja. How dare they take his brothers? How dare they put them all in danger?
Don thought about Mikey as he fought. How he always found humor in any situation. How he could be intelligent if he wanted, but how the thought always seemed to scare him. Donnie laughed out loud as he vaulted himself into the air by his Bo staff.
Maybe he could do it, he wishfully thought.
More ninja appeared out of the elevator. Donnie landed and tried to spin kick his way out of the group, but hands grabbed onto his shell, pulling him, dragging him.
"No!" Donnie cried, reaching out. He felt his weapon get yanked away from him, and it was as if they had snatched his heart and soul from his chest.
He watched as a ninja reared back to knock him unconscious.
Donnie bowed his head as tears flooded his eyes. He couldn't do it. He had failed.
The horrible realization hit him as he held his breath: they were all doomed.
And it was all his fault.
* * * * * * * * * * * * * *

"So, you think we can knock the wall down now?" Mikey asked, after Raph and Leo had explained their plan.
"I've been trying, but it's thicker than I expected," Leo answered.
Mikey opened his mouth to reply, but Raphael cut him off.
"Hold it! Where's that thumpin' noise comin' from, the hall?" Raph pressed an ear to the glass. It wasn't the actual sound he was hearing, since the glass was soundproof. He was feeling the vibrations of the thumping through the floor, which he was still sitting on.
"I don't hear anything," Mikey complained.
"Feel, Doofus," Raph rolled his eyes. "Ya can feel it through the floor."
"Oooohhh," Mikey grinned as he pressed his ear to the floor. Raph smacked him on the back of the head with his good arm.
"Don't be an idiot," Raph growled.
"Feels like fighting," Leo cut in, both hands on the glass floor as well. "You think Donnie's back? Or maybe they put us in a room near their training dojo?"
"I don't think Einstein'd come back so soon," Raph put in. "Not after fallin' out the window and all."
"I don't know," Leo said doubtfully. "How long has it been since we got here?"
"I think I been here over a day," Raph replied, eyebrows knit together. "Wait, wait. How long was I out again?"
"I've been here for, like, two hours," Mikey grinned. Raph smacked him on the back of the head again.
"Well I got news for ya," Raph told him. "Ya've been here longer than that, 'cause they captured ya yesterday. Ya've only been AWAKE for two hours, moron."
Mikey's face fell as that sunk in.
"Oh."
"Guys, stop," Leo said, standing up and squinting toward the door that led into the hallway."Something's going on out there. I wish we could see..."
Suddenly something hit the door, making a loud thump. The turtles looked around at each other, worriedly. The noise had been so loud that time, they could actually hear it. Everything got quiet again, and the vibrations stopped.
The brothers sat back down on the floor and sullenly tried to think of another way out of their prison.