In the Battle TARDIS, Yimi finally stopped writhing. She dropped her hands from her head.
When she got up from the floor and walked over to Jenny, there was a hollow listlessness in her movements and an emptiness inside her eyes. "I am ready to serve," she said in a monotone. "What must I do?"
"About time you came back," Jenny snapped. "I mean — it sucks that I can't have you fawning at my feet anymore, but hollow and empty is better than nothing." She tried twisting a few knobs on the central console and throwing a few switches. Then she gave a shriek of frustration and kicked the console. "Useless thing! Why won't you work?!" She grabbed one of the screens and swung it around. "'Error on final syntax pineapple requiring deference to fishing hook'?! How the hell is anyone supposed to be able to program this stupid thing?!"
"I have had the Zeera woman in my mind, Your Holiness," said Yimi, flatly, as she began adjusting knobs and levers. "I have learned much about how this machine works."
"Oh, you have, have you? Maybe I should have taken you over directly, instead of doing it to these Time Lords." Jenny squeezed her eyes shut, like she was concentrating. Then let out an irritated sigh. "No. It's no good. I can't get control of you without releasing a fraction of my control over the Doctor — and he's just waiting for that split second when I let my guard down."
Yimi ceremonially opened her arms and turned out her palms, the rose colored feathers within shimmering in the lights. "What must I do?"
"Find a way to get Jenny into the vault, for a start!" Jenny shouted. "She may be irritating, but her mind's a lot less slippery than the Doctor's or Bivazeer's. I need someone I can fully control in there. Someone who won't fight back!"
Yimi didn't move. She looked confused. "I don't know what you want me to do, my Lord."
"No, I get that. Think, think, think...!" Jenny's eyes lit up. "Oh, that's interesting. Jenny's trying to hide something from me. She knows how to get me into the vault." Her eyes narrowed, she smiled as she ran around to the far side of the console. "And now I know it, too. Of course! Bivazeer told Jenny that she had some sort of lifeline she could use to drag Lantro out of there. And I can read in Bivazeer's mind that Lantro originally programmed it for her, because it was getting harder and harder to pull her out of the vault. That means it can be altered. Maybe even locked onto someone else." She began frantically flipping switches and pulling levers, but the TARDIS just gave an irritated whine and flashed up an error message on the screen. "Oh, you've got to be kidding me!" She thudded a fist down on the console. "I am going to kill the person who came up with that stupid Oxford Gallifreyan dictionary!"
"These are the controls, my Lord?" Yimi asked, approaching.
"Yes, yes, over here." Jenny gestured at them in disgust. "Jenny's sure they are. They look just like the ones in that room in the Main Complex on Galia-4. All I need you to do is invert it, lock it onto Jenny, then shove her inside the vault. Then I can kill the Doctor and Bivazeer and use Jenny to carry out the real work." She sneered, crossing her arms. "And when I'm done, I'll withdraw my mind from her body and let this TARDIS reconfigure its prison around her, instead. That'll show her."
"Yes," said Yimi, reaching for something she'd tucked inside her pocket earlier. "I will get right to it, my Lord. Right at..."
Without warning, she spun on her heels and leapt at Jenny, yanking the hammer out of her pocket and slamming it down on the top of Jenny's head. The girl slumped to the ground, unconscious.
"You forget, Apos'alu," Yimi told the TARDIS — just in case the Apos'alu could hear. "Unlike these others — I know you. I've felt you inside my mind countless times. That's why it's easier for me to throw you out."
The ship shook again.
Yimi sucked in a sharp breath. "Jenny made her part tamper-proof," she reminded herself, letting go of the hammer and grabbing something else from the toolkit. "That means there's only one place I need to be."
She turned back to the console, pressing a few buttons and flipping a few switches. Took a deep breath.
And with one final push of a button, she vanished.
The Doctor gritted his teeth as he felt the assault ramp up on his mind yet again. No wonder Rassilon had wanted this thing! Even with a human body and after eons of being weakened and restrained, he was using all he had inside him to fight her influence — and felt his control slipping away.
A flash of light burst through the room, and the Doctor winced, shielding his eyes. The birds swiveled their heads round to look — and then squawked in irritation as Yimi stepped out of the light, fire extinguisher in hand. They dove at her, and she directed the nozzle at them and sprayed.
The birds were vexed by the foam — but the steel determination and focus inside Yimi's eyes made them shudder. They fell back, looked at one another...
Then flew off, disappearing from the room as fast as they had appeared.
"How...?" the Doctor asked, looking between Yimi and the birds.
Kardeni leapt at Yimi, then cried out and fell to her knees, hands clutching her head. "Get it out of my mind!" she shouted. "I can't get it out!"
The Doctor just kept staring at Yimi, completely gob smacked. "That's impossible! How did you...?"
"What was it you told me, Doctor?" Yimi said. "The Apos'alu was born on a world destroyed by chaos and by your war. Its powers were the results of evolving in the wake of the destruction brought on by your own weapons." She reached down and unstrapped Seo from the machine. "And it struck me that my people and I have spent thousands of years digging up those same weapons. Our genetics have been changed by their effects as, draft after draft, we have been culled and nearly wiped out so that we might evolve and change and become stronger. The Apos'alu thought of us as nothing. The humans thought of us as slaves. But I know we can be so much more." She lifted Seo out of the machine and set her down gently on the floor. "I can be so much more."
Seo slumped on the ground, her face pale, her eyes closed, as she gasped for air.
Yimi took Seo's place inside the chair.
The Doctor grabbed her by the arm. His teeth were gritted, as the Apos'alu redoubled her attack on his mind to counter Yimi's effect. "Don't," he said. "You're not the Apos'alu, Yimi. You might have scared off her swarm, but that doesn't mean you can defeat her mental powers."
Yimi gave him a sad smile, and removed his hand from her arm. "I know." She strapped herself into the machine. "I'm not as strong as the Apos'alu, nor am I brave as Seo, nor clever as Jenny, nor as effective a killer as Zeera. But we can only drain the Apos'alu while someone is hooked up to the chameleon arch — and I'm ready."
"If this works — and there's no guarantee it will," the Doctor warned, "it will kill you. This chair isn't fitted to your biology. And considering how broken it is already...!"
"I've watched too many others take a bullet for me and my people already," said Yimi. "When Seo met me, I was ready to kill for the sake of my people. Now — I'm ready to die for them." She met the Doctor's eyes with her own. "Allow me to do this, Doctor. I'm ready."
The Doctor, slowly, moved his hand towards the controls to the chameleon arch. He could just about summon the will to press the button and restart the process — but any doubt, any hesitation, and the Apos'alu would swoop in and twist that against him, leaving him petrified.
"Please, Doctor," Yimi said.
He closed his eyes and pressed the button.
Yimi jolted as a surge of electricity ran through her. She gritted her teeth, her eyes focused, but another surge of power ripped a scream from her throat. Slowly, her form began to flicker inside the chair like a candle, then melt like wax.
Seo, from the ground, managed to open her eyes enough to see what was happening. "No. Yimi, don't..."
It was Seo's words that finally made that last resolve slip from the Doctor's mind. He slammed his hand down on the cancel button, praying he wasn't too late. He tried to turn round and release Yimi from the chameleon arch — but that final doubt had spread a thick fog through his mind, and he couldn't keep it out any longer. And even as the Doctor struggled and fought to regain control of himself, he could already feel the Apos'alu taking over and making him completely alter the chameleon arch's programming.
By the time he was done, the Doctor knew, the Apos'alu wouldn't just be free. She'd be more powerful than ever before.
Yimi groaned as she blinked her eyes open. Her whole body ached. Her vision swam as she examined the area around herself — the interior of the Doctor's TARDIS.
Yimi frowned, managing to put aside her aches and pains enough to get to her feet. She looked around herself. Interesting. It wasn't completely unlike the last console room she'd been in — except this one felt warmer, somehow — and hummed with a lot less viciousness and a lot more peacefulness than the other. She found herself almost smiling as she stepped towards the central console, reaching out to it.
"Last time I save someone," came the voice of the Apos'alu.
Yimi turned, but found herself backhanded across the room. Tried to get up, but was immediately kicked down again. The Apos'alu was strong. Fast. Deadly.
"You really had me going there, didn't you?" the Apos'alu said, grabbing her by the neck and throwing her against the wall. "With your sweet eyes and your 'you owe the Doctor something' shtick. Can't believe I fell for it. I blame this hateful human body and its disgusting empathetic emotions."
She dropped Yimi to the ground. Yimi's feathers were already strewn with blood. Her arms and legs were trembling. She would not meet the Apos'alu's eyes.
"I..." Yimi looked around again. "I thought I was..."
"Dying?" The Apos'alu laughed bitterly. "You're about to be." She kicked her again. "Congratulations on sacrificing yourself for nothing, Yimi. Your plan's about to get snuffed out — and so are you."