Kinda the prompt; follows the idea

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"Go for the legs, Dee!" Leo shouted.

Donnie hit a button on his tech bo and hit the monster's legs hard.

Raph used his power punch and knocked the thing down. Mikey wrapped it in his nun chucks just in case.

"Great job team." Leo smiled.

Suddenly, the thing moved and tore itself free from the restraints. It slowly got to its feet and roared.

"Spoke too soon." Leo gulped.

The monster reached a hand down and gripped Donnie tightly. He groaned and the thing tossed him to the side. He broke through the wall and landed against the far one in the next room.

"Donnie!" Raph shouted. "Guys, we have to get him and get out of here! It's too strong now!"

"Leave?! We're not leaving until this thing is down for good. Right, Mikey?" Leo turned to face his orange brother.

"Raphs right, Leo. We won't be able to go home if we don't leave now." Mikey said.

The monster let out a louder roar and swung it's large arm at the three. It hit them with such a force and sent them flying away. Leo skidded against the ground and groaned.

"Ugh. You guys alright?" he looked around for Raph and Mikey.

Raph stumbled toward him. "I'm okay. Mikey?"

Mikey lifted his head and shook it to clear his vision. "I'm all good too, but Dees still in that place. We have to go back."

"No." Leo said firmly. "We'll be on our deathbed if we go back. Donnie can handle it."

"So now you agree when Donnies actually in trouble, huh?" Raph folded his arms.

Leo looked away. "Donnie can handle it. We're going home."

Raph and Mikey hesitantly followed Leo down the closest sewer tunnel.

-----

Donnie groaned. His head felt foggy as he slowly stood back up.

"Where am-" he started to ask, then remembered

He rushed through the hole in the wall. The monster was gone, having left a giant crack in a different wall on the way back to somewhere.

His brothers weren't anywhere around either, and he couldn't here their voices. They had left him there. Donnie raised his left arm, but his wrist tech was broken in his tumble through the wall.

"Okay, just gotta..." Donnie snatched up his tech bo.

He stared down at it for a while. Almost still in shock about his situation. His brothers had abandoned him. But no, they wouldn't do that, right? Maybe the monster had hit them away and they would be back any second.

Sooner or later he realized they weren't coming back. Now driven by a rage beyond his control, Donnie took his tech bo and left the building. He decided on going to Big Mama's, for a reason he would soon find helpful.

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"Leo, listen! The thing has to be gone by now! Why can't we go back?" Raph shouted at him.

Leo spun around. "And risk losing someone else? You listen, Raph. Maybe the monster is gone, but if we go back, so could it."

Splinter walked out of the hallway from the living room. "What's this talk about Purple?"

"_Leo_ decided to leave Donnie behind with a monster we were fighting earlier." Raph glared at the slider.

"Blue, is that true?" Splinter asked.

Leo looked away. "We couldn't risk anyone else."

"You three are going back and looking for your brother. Now!" Splinter shouted.

"But, Splinter-"

"No buts! You will return with your brother if it the last thing you three do!" Splinter commanded.

-----

Donnie stormed into Big Mama's office. "Big Mama." he greeted solemnly.

"If it isn't the turtle who made that splendiforous contraption to capture those pesky bugs. What brings you up here?" Big Mama wondered.

Donnie went up to her desk and reached over it to grab her collar. "I need you to get my brothers here."

"Oh? And why might that be, hm?" She asked.

Donnie released her shirt. "They abandoned me."

"Dear, what a terrible fate. I'll get them here for you if you agree to make me more splendiferous machines." Big Mama whispered. "What do you say?"

Donnie didn't waste a second to nod. "You got yourself a deal."

"Very good." Big Mama clapped her hands.

Two large yokai walked into the room. One a fox, the other an owl.

"Yes, Mum?" the fox asked.

"This turtly-boo and I made a deal. Get his brothers here unharmed." Big Mama stated.

Donnie turned to face them. "They should be in the broken building at the dock. If Splinter made them come find me, which he probably did."

The fox and owl nodded and left quickly into the elevator.

Donnie turned back around to Big Mama. "Unharmed and in the Battle Nexus." he straightened himself. "No tricks."

"Not when you're this enthusiastic about getting rid of your bimbly brothers." Big Mama giggled.

-----

"I still don't see why Splinter made us come back here." Leo lifted another chunk of rubble.

"Because Donnies here. And probably hurt." Mikey answered.

"Guys, didn't Donnie get thrown over there?" Raph pointed to the broken wall.

Mikey and Leo scrambled over the rubble over to the wall. They walked cautiously inside and looked around. Donnie was nowhere inside.

"Hey, Raph, I don't think-" a cloud of smoke surrounded Leo.

Leo coughed and his vision started to get blurry. Mikey collapsed from it beside him. Leo tried to call out, but his voice wouldn't come. He gave in and fell.

Leo blinked open his eyes and groaned. He rubbed his forehead. Raph paced nearby and Mikey had curled his legs close against his plastron with his head on Leo's shoulder.

"Where are we?" Leo asked quietly.

"We don't know either." Mikey whispered. "One second we were looking for Donnie and the next we were here."

Leo looked around the cold, damp room. There was a bench we was leaning on. And what looked to be weapon holders above that. The door had only small cracks to let light in.

-----

Donnie waited patiently for Big Mama's bellhops to return. He had made little conversation with her in the meantime.

Eventually, the fox came through the elevator doors. "The turtles were captured, Mum. They were right where he said they were."

"Very good. You may return to your regular post now." Big Mama smiled.

The fox nodded and left.

"Can I make sure they put them in the right place?" Donnie wondered. "Wouldn't want them escaping, now do we?"

"Of course not, turtly-boo. I'll even come with you." Big Mama laughed.

The duo left the office and made their way toward the Battle Nexus gateway. Donnie glanced suspiciously at the two yokai on either side of the portal before he went in. Big Mama guided him through the twisting hallways until they reached the cells.

"That one." she pointed to one in a corner. "Be quick. Big Mama already has her first tech request."

Donnie nodded and walked toward the cell. He peeked through the small bars, laughing a little when he saw his brothers.

"How's it feel to be trapped, huh?" Donnie asked.

The three of them leaped to their feet at his voice.

"Dee? But..." Leo trailed off.

"After you abandoned me, I came to Big Mama's." Donnie told them.

"It was an accident, Donnie, promise!" Mikey shouted desperately.

"None of you deserve to call me that. Brothers who _don't_ abandon me can call me that. I go by something new. Something you especially don't deserve to know. Welcome and good luck in the Battle Nexus." Donatello walked away.

Leo, Mikey, and Raph tried to call him back, but he was too far away to hear them now.

-----

"I can't believe Donnie went to Big Mama of all people. He could've gone to Draxum or even..." Leo trailed off.

Mikey sobbed into Leo's shoulder.

"We just have to get out of here and convince him it was only an accident. That we didn't mean to leave him behind." Raph said.

"I should've listened to you." Leo whispered. "None of this would be happening if I had only listened to you in the first place."

Raph glanced down at him. "I'm glad you're admitting it, but it was an honest mistake. Donnie just took it the wrong way is all."

"No, no that's not true. We left him there! He..." Leo paused and took a deep breath. "He could have _died_. And it's all because I thought he could handle it on his own."

Raph didn't say anything back. Suddenly, the door behind him opened and a fox yokai appeared.

"Big Mama requested you in her office." the fox said. "Don't try any funny business. Donatello is making Mum some extra security."

Leo, Mikey, and Raph hurried out the door and followed the fox all the way out of the Battle Nexus and up to Big Mama's office.

"There you are turtly-boos! Good for you to join us!" Big Mama laughed. "I got you three seats."

The trio sat in the seats in front of her desk.

"Why'd you call for us?" Raph asked cautiously.

"Because Draxxie came looking for you three. _Four_, I mean. This betrayal is quite amusing." Big Mama giggled.

Leo looked away and Mikey narrowed his eyes.

Donatello appeared in the elevator doorway. "I finished the security you requested."

"Oh goody!" Big Mama smiled. "Since Draxum came by for you four, we might have to pause the next request and make sure that he doesn't come back. A solution?" she turned to Donatello.

"Give them to him." He said simply.

"That means you're changing your side of the deal. Which also means I get to change mine. I give Draxum your brothers, and you have to work by my side. Deal?" Big Mama held her hand out.

Donatello walked over and shook it. "Deal. No tricks."

"As I said before, there won't be any tricks. It's quite amusing to see you want revenge on your brothers this much." She laughed.

Donatello glanced at the three's shocked faces with no emotion on his.

His brothers would have to face it. The Donnie they knew was gone, replaced by Donatello, abandoned and looking for revenge. Any way he could get it.