Leonardo couldn't believe it.

He just couldn't believe it.

He had just started to have the tiniest bit of faith in Karai, and then this happened. She was actually playing along with the Ronin's game.

Mikey, of course, wanted to give her the benefit of the doubt. That was something that Leo had always loved about Mikey – he was so generous.

But it also kind of made him an idiot.

Leo put a hand over his face. He was starting to think more like Raph, and he wasn't sure whether or not that was a good thing.

They walked into the lair, where Splinter sat on the couch, apparently meditating, and Karai paced across the den. She looked up and smiled at them – she smiled. Leo frowned in return.

Karai tilted her head. "What happened?"

Splinter looked up and rose from the couch and walked over.

"April found out something very interesting," Leo said. "April?"

April flushed. "Um…well…I…"

"The Kraang are working on the Hamato genocide project," Raph said gruffly. He pointed a finger at Karai. "You said you weren't gonna tell them to."

Karai's mouth fell open. "Are you serious? They're working on it?"

"Stop playing dumb, Karai. Stop playing us."

"But – I didn't tell them to. I swear I didn't."

"And we're supposed to trust you how?" Leo said.

Karai held up a beaker full of shimmering liquid. "I got the retro-retro-mutagen for Donatello, just like I said I would."

"Yeah? How do we even know that's what that actually is, huh? How do we know that's not part of the Ronin's scheme, too?"

"You really think I'd work with that lunatic?"

There was a moment of silence. Finally, Splinter drew a deep breath and sighed. "Karai, all evidence here suggests that this is precisely what you are doing. I do not doubt that you have what you think is a good reason – "

"I did not tell the Kraang to start working on that project. Ronin must have gone over my head somehow."

"Yeah, that would be a perfect excuse if we didn't know he made you his liaison with the Kraang," Leo said.

I can't believe I started to trust you again, Karai.

"I'm telling you," Karai said, a note of desperation in her voice, "I didn't do it! Ronin might be crazy, but he's smart enough that he could find a way to talk to them directly. He must not have actually trusted me to go through with it."

"Well, you can hardly blame him for not trusting you," Raph said.

"STOP IT, EVERYONE!" Mikey threw his nunchuks down on the floor.

Everybody stood stock still and stared at him. Mikey's face was red and his eyes were watery, but on top of that, there was a look of desperation and anger that vaguely reminded Leo of Mikey's breakdown after Donnie was un-mutated.

That's all this is, Leo realizes. He just wants Donnie back, and trusting Karai is the only way he can get that.

That's the only way any of us can get that.

"We. Are. A. Family," Mikey said. "We hafta trust each other. If we don't have that, then what do we got? Nothin', that's what – just a sad sack of sorry losers."

"Just stop it, Mikey," Raph said. "You have no idea what's really going on here."

"I do too!"

"Mikey's right, you know," April said. Her voice was quiet, but somehow seemed even louder than Raph's shouting.

Leo drew a deep breath. "Karai, will you help us destroy the Kraang's project?"

"If that's what it takes, I'll go in and destroy all the research by myself," Karai said. "I swear that I'm telling the truth. You don't have to trust me, Leo. Just believe me this one time."

"Trust, believe – sounds kinda like the same thing to me," Raph said.

"You don't have to trust somebody to believe them," April said.

Yeah, but it sure helps. Leo put his hand on his face for a moment. "Okay, Karai, fine. I believe you this time. I'll even believe you when you say you actually got the retro-retro-mutagen." He ignored the look of disbelief on Raph's face and looked over at Splinter.

Splinter nodded.

It didn't necessarily make Leo feel any better, considering that Raph had mentioned that Splinter was, well, a bit of a sap when it came to Karai. At first, Leo had been furious over the comment, but now, he realized the truth in it. He could hardly fault Splinter for that, though.

He had a terrible sinking feeling inside. How much of his willingness to give her a second – third – chance, despite not trusting her, was because he still sort of liked her? How much of his anger at her was because he liked her and she had hurt him? For the first week or so after Karai's initial betrayal, he thought he was done with any kind of feelings for her whatsoever.

And it was just as well, considering that she was his sister.

But slowly, the feelings crept back in, unbidden. He found himself wishing that maybe, somehow, she would prove herself trustworthy again – though he had no idea what that would entail – and that their friendship would be able to grow again, not stunted by distrust or fear.

And who knew where that friendship might lead…

What he just giving her this third chance because he was desperate to find a reason to trust her again? Was he just thinking with his stupid teenage hormones, or was he actually using his brain? He'd screwed up his leadership on account of Karai more than once – heck, practically since he met her – and it had gotten his team into too many close calls.

But this time, it would be different. They'd be going into the Kraang base as a full team – surely five of them would be able to outsmart any betrayal Karai might have in store for them.

Particularly if one of the five happened to be the smartest turtle in the universe.

"April," Leo said, "do you know how long it will be before the Kraang have the Ronin's tech ready for him?"

April nodded. "They said that they have the scanning device ready now, but that it will still take them about two weeks before they have the genetic research complete. At least, I think that's what they said…it all sounded, you know, really Kraang-y."

"All right, then. Karai, you and I are going to go test the retro-retro-mutagen on Xever. If it's a success, we'll re-mutate Donnie. He can come with us on the mission and be doubly sure that all of the data on April and all of the data for the Ronin's project is totally wiped from the system. Then we'll blow the scanner – and the whole place, if we can."

Mikey's face shone. "Donnie's gonna come on the mission with us?"

Leo's heart sank. He hadn't wanted to plant false hope in Mikey. "Assuming the serum works, yes. If not…we'll improvise, okay?"

"Leonardo," Splinter said, "even if the serum is a success, Donatello may need time to rebuild his strength. He may not be in any condition to fight."

"That's why we're bringing April, too. And that's why Karai and I are going to test the serum on Xever before daybreak. We need to give Donnie at least a week of recovery, and I don't want to push the deadline on this at all."

"Hmm." Splinter's expression was disapproving.

"Look, Sensei, I know it's a risk, but if I can have Donnie with me on this mission, we're much more likely to succeed. Nobody knows how the Kraang operate like Donnie does."

"Very well," Splinter said. "Go, then."

"That retro-retro-mutagen better work, Karai," Raph said. His voice had an edge to it. Raph probably meant it as a threat, but Leo could hear the touch of desperate hope in it too.

"Well, the Kraang are pretty good at everything except for perfecting the mutagen and killing you guys," Karai said. "I think it will work just fine."

"Come on, Karai," Leo said. "Let's go to Donnie's lab. Bring the beaker."

"You know, that's a weird name for those things," Mikey said. "They look nothing like beaks."

Once Leo and Karai were in the lab, Karai shut the door behind them. Leo's stomach went cold, and he mentally prepared himself to reach for his katanas.

Karai set the beaker down on Donnie's desk. "Thank you," she whispered. She threw her arms around Leo and hugged him.

He flinched. His mind was torn between the desire to return the embrace, embarrassment and excitement, and the keen need to be prepared for any trickery she might be up to. He could feel himself blushing furiously.

Karai released him from the hug. She cleared her throat. "So. What do we need to do?"

"Well, we need to get Donnie's dart gun, and load up a couple of syringes with that stuff."

"Where are the syringes?" Karai said.

"I think they're in that top drawer. Donnie keeps a lot of medical type junk over there." Leo saw the dart gun sitting on top of a cart on the other side of the room. He was hesitant to turn his back to Karai, so he slowly walked over to the dart gun, keeping his body at a partial angle to her so he could keep an eye on her.

She, on the other hand, seemed to have no problem turning her back to him.

Of course she trusts me, Leo thought. She trusts me to be a total schmuck. Angry heat rose to his face.

After they had finished the preparations, they left the lab. "Well," Leo said, "don't wait up for us, I guess."

April was already passed out asleep on the couch. Mikey sat next to her, nodding slightly. Raph sat on one end of the other couch reading a comic book or something, and Splinter sat solemnly at the other end of the couch, stroking his beard, obviously deep in thought.

He turned his head to them. "Good luck, my children."

Leo nodded. "All right, Karai. Let's go."

The two of them jumped the turnstiles and headed to the surface.