Chapter 6: The Poison Sky

While the Doctor and Eris floundered about the car - him diving underneath to disconnect the exhaust and her trying to pick the door locks - Sylvia Noble had a far more effective idea. She ran from the house, wielding an axe, and slammed the bonnet shut before swinging the weapon at the windscreen. It shattered, and the others stared for a moment, dumbfounded.

"Well, don't just stand there. Get him out."

They moved to help him, finally managing to unlock the door.

"Thanks."

Donna stared at her mum in disbelief. "I can't believe you've got an axe."

She shrugged, like the reason was obvious. "Burglars."

The Doctor, aware of the quickly thickening fog, gestured for them to get through the doorway.

"Get inside the house. Just try and close off the doors and windows."

A whistle cut through the air, and he turned to see Eris hailing a cab - Ross was behind the wheel.

"Doctor. This is all I could find that hasn't got ATMOS."

"Donna, you coming?"

"Yeah."

Sylvia's jaw twitched. "Donna. Don't go. Look what happens every time that Doctor appears. Stay with us, please."

Wilf, however, had other ideas. "You go, my darling."

"Dad!"

"Don't listen to her. You go with the Doctor. That's my girl."

Donna got into the backseat with the Doctor, waving goodbye as they rounded the corner.

Even with the lack of visibility, the journey was smooth, and they were quickly back at the road that connected the alleyway to the outside car park of the ATMOS factory. Hearing the distant noise of soldiers mobilising, the Doctor took charge - naturally.

"Ross, look after yourself. Get inside the building."

Eris moved to join him. "I'll come, start filling the Colonel in on the Sontarans. It's all well and good having a file - which somehow I doubt he's actually read - but speaking to someone with experience of them will be far more useful."

Donna pulled a face. "So what are we doing?"

The Doctor nodded back towards the alleyway. "Going back to the Tardis. You're not safe out here."

"But Ross-"

The young soldier shook his head. "It's my job to be out here, ma'am. The Colonel will have my arse if I duck out of my responsibilities."

Eris slung an arm around his shoulders, and even through the haze the others could see his cheeks darken.

"Besides, I'll look after him. Catch up with us as quick as you can."

The two of them set off towards the base, the sound of Ross' voice fading as they got further away.

"Greyhound Forty to Trap One. I have just returned the Doctor and Eris to base safe and sound. Returning to headquarters now. Over."

Relieved, Colonel Mace responded. "Trap One. Received. Over."

Having heard the interaction - and knowing that she would need to keep her cover - Martha's clone rushed into the room, taking care to make it look like she'd just received the information she was about to deliver.

"Sir. Message from the Doctor. He says Code Red Sontaran."

He nodded, not suspecting a thing, and opened all the radio channels.

"All troops. Code Red Sontaran. Code Red Sontaran."

As they reached the mouth of the alleyway, Donna could feel the air in her lungs thickening, and she grimaced.

"The air is disgusting."

"It's not so bad for me. Go on, get inside the Tardis. Oh, I've never given you a key." The Doctor rummaged in his pockets, finding the key that he had been planning on giving to her anyway. Somehow, he'd kept forgetting about it - or something had gotten in the way. "Keep that. Go on, that's yours. Quite a big moment really."

She rolled her eyes. "Yeah, maybe we can get sentimental after the world's finished choking to death."

"Good idea."

"Where are you going?"

"To stop a war."
He turned and ran towards the factory, leaving Donna to let herself into the Tardis and close the door behind her.

When he reached the headquarters, it was clear that the Colonel had been arguing with Eris - and he hadn't won. The man was staring sulkily at the large screen, snapping orders at the group of workers buzzing about the smaller computers. In contrast, his daughter was talking animatedly to Ross and some of the other soldiers about the information they had gathered while they were away.

"Right then, here I am. Good. Whatever you do, Colonel Mace, do not engage the Sontarans in battle. There is nothing they like better than a war. Just leave this to me."

He huffed. "And what are you going to do?"

"I've got the Tardis. I'm going to get on board their ship."

In the corner, Martha grabbed her phone and snapped a quick message to Grey and Harris. She knew they would act quickly - she just had to hope they were fast enough. The Doctor turned to her, and she shoved the phone away.

"Come on. Eris, you coming?"

She didn't look up. "Nah, I'm trying to hack through some of the computer work the Sontarans put in place around the factory. Hopefully we can interfere with things from here while you're up negotiating. See you in a bit."

He winked at Colonel Mace, then he and Martha set off.

Martha's clone had to school her expression back to one of shock and confusion as the Doctor stopped dead, staring at the spot where the Tardis had been parked. The key word being 'had'.

"But where's the Tardis?"

He paced about for a moment, sniffing deeply. "Taste that, in the air. Yuck. That sort of metal tang. Teleport exchange. It's the Sontarans. They've taken it. I'm stuck on Earth like, like an ordinary person. Like a human. How rubbish is that? Sorry, no offence, but come on."

"So what do we do?"

"Well, I mean, it's shielded. They could never detect it."

It was then that she noticed he was looking at her oddly. "What?"

"I'm just wondering, have you phoned your family and Tom?"

"No. What for?"

"The gas. Tell them to stay inside."

She shrugged. "Course I will, yeah but, what about Donna? I mean, where's she?"

"Oh, she's gone home. She's not like you. She's not a soldier. Right. So. Avanti."

Outside the Rattigan Academy, the students had congregated on the lawn, staring aghast at London. Their usual view of the western parts of the city - the Post Office tower, the London Eye - were rapidly vanishing under the veil of smog.

Stepping out to join them, Luke scoffed.

"Leave it. Turn away. Civilisation is falling."

One of the young men turned to look at him, very pale.

"But it's all over the news, sir. It's everywhere. Paris and New York."

"It's time I told you. All of you. It's time I revealed what our work has been for."

Striding back into the headquarters with his first priority being to update Eris on things, the Doctor patted the Colonel on the back.

"Change of plan."

"Good to have you fighting alongside us, Doctor."

"I'm not fighting. I'm not-fighting, as in not hyphen fighting, got it? Now, does anyone know what this gas is yet?"

Martha shook her head. "We're working on it."

Eris frowned up at him, but the slightest of head shakes shut down her question. She continued.

"By the looks of it, it's harmful, but not lethal until it reaches eighty percent density."

A uniformed blonde next to her gestured towards a series of screens displaying news from around the world.

"We're having the first reports of deaths from the centre of Tokyo City."

"And who are you?"

"Captain Marion Price, sir."

"Oh, put your hand down. Don't salute."

The Colonel cut in. "Jodrell Bank's traced a signal, Doctor, coming from five thousand miles above the Earth. We're guessing that's what triggered the cars."

"The Sontaran ship."

"NATO has gone to Defcon One. We're preparing a strike."

Before he could explain just how dreadful that idea was, Eris groaned and got out of the seat she'd borrowed.

"So you didn't listen to a word I said earlier. Right, gotcha, that's really helpful. Striking against the Sontarans is never going to work, they're quite literally born and bred for war. Believe me, you don't stand a chance."

Her dad moved to stand next to her. "Nuclear missiles won't even scratch the surface. Let me talk to the Sontarans."

The Colonel raised an eyebrow. "You're not authorised to speak on behalf of the Earth."

"I've got that authority. I earned that a long time ago." And before the man could argue any more, he jammed the sonic into the communications system, overriding the settings and broadcasting into space. "Calling the Sontaran Command Ship. Under Jurisdiction Two of the Intergalactic Rules of Engagement."

An image flickered onto the screen; Staal's exposed head, obscuring most of the movements of the other Sontaran soldiers in the background.

"This is the Doctor."

"Doctor, breathing your last?"

Mace looked slightly nauseated. "My God, they're like trolls."

"Yeah, loving the diplomacy, thanks. So, tell me, General Staal, since when did you lot become cowards?"

Staal visibly bristled. "How dare you!"

"Oh, that's diplomacy?"

"Doctor, you impugn my honour."

"Yeah, I'm really glad you didn't say belittle, because then I'd have a field day. But poison gas? That's the weapon of a coward and you know it. Staal, you could blast this planet out of the sky. And yet you're sitting up above watching it die. Where's the fight in that? Where's the honour? Or… Are you lot planning something else, because this isn't normal Sontaran warfare. What are you lot up to?"

"A general would be unwise to reveal his strategy to the opposing forces."

"Ah, the war's not going so well, then. Losing, are we?"

"Such a suggestion is impossible."

Mace glanced across at Eris. "What war?"

She leant against the computer bank, arms folded. "There's been a war raging on between the Sontarans and a blobby green species called the Rutans for… oh, millenia now."

The Doctor nodded. "Fifty thousand years of bloodshed, and for what?"

"For victory. Sontar-ha."

And the Sontarans broke into their monotonous war cry, stamping their boots and slapping their fists in rhythm.

"Sontar-ha. Sontar-ha. Sontar-ha. Sontar-ha. Sontar-ha."

"Give me a break."

Rolling his eyes, the Doctor grabbed the sonic and switched the channel over to a cartoon.

Eris scrunched her nose.

"Is this what passes for kid's TV these days? The last thing I saw was a random episode of The Clangers."

Next to her, Ross grinned. "Yeah, I remember watching that as a kid. My brother and I used to love it."

Nerves wearing thinner by the second, the Colonel smacked his hands against the desk.

"Doctor. I would seriously recommend that this dialogue is handled by official Earth representation."

Not replying, he simply switched back to the communications channel, where the Sontarans had quietened down.

"Finished?"

Staal sneered - it didn't seem that his face was capable of many other expressions. "You will not be so quick to ridicule when you'll see our prize. Behold. We are the first Sontarans in history to capture a Tardis."

The scanner panned round to display the blue box, and Eris groaned internally. So that was half the reason he was still here.

"Well, as prizes go, that's noble. As they say in Latin, Donna nobis pacem."

She glanced over at him, and the rest of the tale fell into place. Donna had been on board, and so she was now stuck in the heart of the Sontaran battle fleet.

"Did you never wonder about its design? It's a phone box. It contains a phone. A telephonic device for communication. Sort of symbolic. Like, if only we could communicate, you and I."

"All you have communicated is your distress, Doctor."

"Big mistake though, showing it to me. Because I've got remote control."

A note of fear crept into the alien's voice. "Cease transmission!"

And the screen went blank.

"Ah, well."

Mace glowered at him. "That achieved nothing."

"Oh, you'd be surprised."

As the Colonel stormed off to speak to Martha, Eris lowered her voice.

"What else is wrong?"

"It's Martha. I'm pretty sure that's a clone."

"Well, that's probably the route the Sontarans would go down for infiltration, given their own method of birth."

"My thinking exactly. But I don't think she knows that we know just yet, so keep an eye on her. I still don't know what they're using her for."

Standing in the centre of the academy laboratory, Luke spread his arms wide.

"All this stuff we've been building. All this invention. Where's it been heading? Gravity densifiers, hydroponics, atmospheric conversion, ecoshells. More than enough to build a brand new world."

"Luke, we haven't got time for this. I've got to find my parents."

"Oh, but this isn't just theory. I'm talking Planetfall, for all of us. A brand new start for a brand new human race. Look." He flicked a switch, and a holographic image of a planet appeared. "A new world, far out, beyond Alpha Geminorum, just waiting for us. Its official destination is Castor Thirty Six. I think of it as Earth Point Two. I did wonder about Rattigan's World, but we can take a vote on that."

The other young man stared at him blankly. "What the hell are you on about?"

"This is where we're going. I have partners willing to take us there."

A pretty brunette scoffed. "Oh, he's lost it. I haven't got time for this."

"Excuse me, I haven't finished. Where are you going?"

"To find my brother."

"I didn't say you could leave."

"I told him to put ATMOS in his car. I've got to go and help him."

Luke took the gun from his belt, holding it in shaking hands. "Stay where you are."

"What do you think you're doing?"

The boy got between them, holding his hands out. "Luke, put that down."

"But, I did this for you, don't you see?" He looked around at the little cluster of his students, nearly two dozen of them in total. "We've spent all our lives excluded. The clever ones. They've laughed at us and pulled us down, those ordinary people out there. Those cattle. This is our chance to leave them behind."

"You mean you want them dead?"

"And I chose you to survive. With Planetfall we can start again. We can build and breed, we can prosper, we can do anything."

The girl's jaw dropped. "We're going to breed?"

"I've designed a mating program. I've planned the whole thing."

"Well then, shoot me." And she turned to leave.

"Stay where you are. Stay where you are, I said. Stay where you are."
But they had finally stopped listening. The rest of the students followed, flowing out of the door in a stream of red polyester until there was only one student left, standing in the doorway with a look of pity on his face.

"Stay where you are. That's an order!"

"Castor Thirty Six? You're just sick." And he walked away too, leaving the hyperventilating young man alone.

"I guess that just proves it. I'm cleverer than you. I'm cleverer than everyone, do you hear me? I'm clever!"

The sound of the phone ringing was only just audible above the news - and it still took Sylvia a few moments to dig it out from underneath one of the sofa cushions. How it had ended up there, she would never know.

"The United Nations has issued a directive worldwide, telling urban populations to stay indoors. Those in rural areas are being ordered to stay away from all major cities. There are reports from every country in Europe of thousands of people walking across country to escape. And on the Eastern seaboard of America it's said to be reminiscent of Dunkirk, with boats taking refugees out into the Atlantic."

She answered.

"Mum, you all right?"

"Donna. Where are you, sweetheart?"

Kneeling at the patio doors, Wilf looked up. "Is that her?"

"Oh, just finish the job. Your granddad's sealing us in. He's sealing the windows. Our own house and we're sealed in. All those things they said about pollution and ozone and carbon, they're really happening aren't they?"

"There's people working on it, Mum. They're going to fix it, I promise."

"Oh, like you'd know. You're so clever."

The sneer in her mother's voice stung. "Oh, don't start. Please don't."

Then came the voice cracking, which was almost worse. "I'm sorry. I wish you were here."

She heard the phone changing hands, and her grandad speaking softly.

"Now, come on, Sylvia. Look, that doesn't help. Donna, where are you?"

At any other time, the prospect of explaining the Tardis to him would have been hilarious.

"It's sort of hard to say. You all right?"

"Yeah. Fighting fit, yeah. Is he with you, the Doctor?"

"No. I'm all on my own."

"Look, you promised he was going to look after you."

"He will, Gramps. There's something they need me to do. I just don't know what."

"Well, I mean, the whole place is covered. The whole of London, they're saying. The whole, the whole world. It's the scale of it, Donna. I mean, how can anyone stop that? How can one man stop all that?"

"Trust me. He can do it."

"Yeah, well, if he doesn't, you tell him he'll have to answer to me."

She managed a slightly watery laugh. "I think he'd have to answer to Eris as well. But I'll tell him. I will. Just as soon as I see him, I'll tell him."

Martha's clone brought a clipboard over to the Doctor. Her commanders had decided it was best to feed them little snippets of information: that way, they could control what they knew and when. It was a far better option than letting the humans stumble into their entire plan by accident. Especially with the Doctor around - he was the one thing that gave the humans a slight chance of gaining the upper hand.

"There's carbon monoxide, hydrocarbons, nitrogen oxides, but ten percent unidentified. Some sort of artificial heavy element we can't trace. You ever seen anything like it?"

He shook his head. "It must be something the Sontarans invented. This isn't just poison. They need this gas for something else. What could that be?"

Captain Price called out. "Launch grid online and active."

Colonel Mace tensed. "Positions, ladies and gentlemen, Defcon One initiatives in progress."

His eyes widened. "What? I told you not to launch."

"The gas is at sixty percent density. Eighty percent and people start dying, Doctor. We've got no choice."

"Launching in sixty, fifty-nine, fifty-eight, fifty-seven, fifty-six. Worldwide nuclear grid now coordinating. Fifty-four, fifty-three, fifty two…"

With an expression that made the Colonel distinctly afraid that she was going to punch him, Eris squared up to him.

"You know, I genuinely hope the Sontarans are ahead of you. A snowball has a greater chance in Hell than those missiles do of even coming close to those ships. Whatever the outcome, this is a decision that you will regret for the rest of your days - and there may not be many of those left. Nuclear warfare will kill you just as easily as this gas will, and the Sontarans will get what they want either way."

Captain Price continued. "North America, online. United Kingdom, online. France, online. India, online. Pakistan, online. China, online. North Korea, online. All systems locked and coordinated. Launching in ten, nine, eight, seven, six, five, four, three, two, one."

Unnoticed, Martha stood with her back to the computers, activating a shortcut on her phone. It had access to the launch system, and came up with two buttons - yes and no. Green and red. She hit the red button with her thumb.

"Zero."

And the screens went black.

There was a moment of silence, in which Mace's face got progressively redder.

"What is it? What happened? Did we launch? Well, did we?"

"Negative, sir. The launch codes have been wiped, sir. It must be the Sontarans."

"Can we override it?"

"Trying it now, sir."

The Doctor didn't even try to hide his relief, and allowed his mind to wander. "Missiles wouldn't even dent that ship, so why are the Sontarans so keen to stop you?" He glanced across at Martha. "Any ideas?"

She shrugged, a little defensive. "How should I know?"

A platoon of soldiers were patrolling the factory, most of them grumbling about the lack of one person - Jenkins. He was meant to be in charge of their section, but had apparently been held back at HQ by request. The fact that this request had come from a pretty woman, according to those who'd seen her, only made them more jealous. Adams, who'd taken charge in his place, tried to keep them under control.

"It's stinking out there." He heard footsteps and faltered. "Shush. Keep it down lads."

Sontarans appeared around the corner. Having been given a basic briefing over the radio, he switched the communication channel on.

"Enemy within. At arms. Greyhound Forty-One declaring Absolute emergency. Sontarans within factory grounds. East corridor, grid six."

Hearing this, Colonel Mace responded.

"Absolute emergency. Declaring Code Red. All troops, Code Red."

The Doctor was quiet, but his voice was steely. "Get them out of there."

"All troops, open fire."

As the sound of gunfire was heard, Jenkins paled.

"That's my section. I'm forty, forty-one through sixty-five are my men." And he grabbed the radio from his boss, ignoring the look on the older man's face.

"Guns won't work. Inform all troops, standard weapons do not work. It's called a cordolaine signal."

The sound of the guns faded to nothing, and Eris moved to support Ross, keeping the man upright as he shook. The Colonel took back the radio.

"Greyhound Forty-One, report. Over. Greyhound Forty-One, report. Greyhound Forty-One, report."

Unable to take it any longer, Eris ripped the radio from his hands and grabbed the man's collar, pulling him down to her height. The soft venom in her voice made his knees quake.

"He wasn't Greyhound Forty-One. His name was Michael Adams. Had I not overruled your orders and kept Ross here, my newest friend would be going cold on that factory floor. Now listen to me, and get them out of there!"

She released him, and he did what she said without delay.

"Trap One to all stations. Retreat. Order imperative. Immediate retreat."

Unfortunately, the massacre was already well underway.

"Retreat. Retreat."

The UNIT soldiers had very little chance; those who did escape were only able to do so out of sheer luck. They were no match for the Sontarans, whose military organisation was beyond anything they could ever have imagined. As their one-time colleagues scattered, Grey and Harris snapped to attention as Commander Skorr approached.

"Reporting for duty, sir."
He shot them without word before moving onto some more entertaining targets.

"This is too easy. They're running like slimebait from a speelfox. This isn't war, this is sport!"

Mace slammed his hands down on the desk. "They've taken the factory."

The Doctor sighed. "Why? They don't need it. Why attack now? What are they up to? Times like this, I could do with the Brigadier. No offence."

"None taken. Sir Alistair's a fine man, if not the best. Unfortunately, he's stranded in Peru."

Eris rolled her eyes, and disappeared into the back office as Captain Price turned around.

"Launch grid back online."

The sentence had barely left her mouth when the screen went blank again. She tapped at a few of the keys, with little success.

"They're inside the system, sir. It's coming from within UNIT itself."

"Trace it. Find out where it's coming from, and quickly. Gas levels?"

"Sixty six percent in major population areas, and rising."

Returning to the ship, Skorr rubbed his hands together gleefully.

"Commander Skorr reports victory with many glorious deaths."

Luke teleported in, dry eyed. He couldn't risk crying in front of his bosses.

"Sorry to report, sir, I've failed. They wouldn't come. The students, they didn't have the imagination to believe."

Staal shrugged. "A pity. We've lost our target practice."

"What do you mean?"

"Upon arrival on board this ship, your students would have been shot down. Perhaps they were more clever than you thought."

"You promised-"

"There was no Planetfall. Castor Thirty Six, indeed. We only needed you for installation of the ATMOS system."

He could feel angry tears building up again. "No, but I'm on your side. I did everything you wanted. And it's not ATMOS system. That's a tautology. It's just ATMOS."

Staal sneered, gesturing to one of his soldiers. "Execute him."

Realising that he was still on the teleport pad, Luke smacked the button and vanished before the Sontarans could fire.

"A coward's retreat. Now close all teleport links to Earth. Isolate them as they perish."

"Oi, Colonel - get in here. Now."

Mace raised an eyebrow at the Doctor. "Your daughter really ought to learn some respect, you know. Some people may take offence to her attitude."

The Doctor snorted. "She's over 430 years old - I'm sure she can handle anyone who takes issue with her. Come on. It's best not to keep her waiting."

The two men filed in to see Eris sitting cross legged on the Colonel's desk, a phone in the palm of her hand and a slight smile at the corners of her mouth.

"Ah, they're here now. You're on speaker, Alistair."

And a very familiar voice came through the speaker - slightly changed with age, the Doctor thought, but unmistakeable nonetheless.

"Ah, Colonel. I hope you're handling the Sontarans alright over there. Dreadfully sorry I can't be there, you know, but going up in the helicopter in all this gas would be a death wish. How are things, Doctor?"

As the Colonel's jaw dropped and he snapped to attention, the Doctor grinned.

"Hello Brigadier, it's been far too long."

"Yes, hasn't it just. What's the situation?"

"Oh, nothing we can't handle."

The Colonel recovered himself. "Sir, we're working on getting around the cordolaine signal the Sontarans are using to interfere with our weaponry, and the nuclear missiles are-"

He was cut off. "Who authorised the use of nuclear missiles? It certainly wasn't anyone from my department."

"The UN, sir. They've authorised firings from every country with nuclear capability."

Eris' grin widened as the Brigadier grumbled. "Oh, blasted political fools. Always getting above themselves and resorting to the worst option before thinking through the others. Colonel, listen to the Doctor and Eris. Their experience with these creatures will prove valuable in besting them." There was a crackle, and what sounded like faint swearing. "I'll have to go, the lines are being interfered with. It's bad enough having worldwide gas emissions to deal with, but the creatures who I came down to deal with haven't laid off either! You'd think aliens would have a sense of good timing."

Her face fell a little. "Alright, goodbye Alistair. I'll get in touch again once this is sorted."

"That had better be a promise, my dear."
"Nothing in the universe could stop me."

And the line went dead.

The Colonel looked at her, baffled. "I… I've never heard anyone speak to the Brigadier like that."

The Doctor, on the other hand, just rolled his eyes. "You're a worse flirt than Jack."

She pulled a look of mock horror. "I take offense to that! Besides…" she winked at the Colonel "you should have heard us back in the old days."

Groaning, the Colonel tried to get them back on track to the situation.

"Why are they defending the factory only after we were inside?"

Eris raised an eyebrow. "Isn't it obvious? Because they wanted UNIT here. You gave them something they needed. Something that's now hidden inside the factory, tucked away safe and sound. Something precious."

"We've got to recover it. This cordolaine signal thing, how does it work?"

"It's the bullets. It causes expansion of the copper shell."

"Excellent. I'm on it."

The Doctor felt like tearing his hair out. "For the billionth time, you can't fight Sontarans!"

But he had already left, barking orders at his soldiers.

"Phone, gimme."

She handed it over. "You could at least say please."

"Keep an eye on Martha. I'm calling Donna."

It took a couple of rings before she picked up.

"What's happened? Where are you?"

"We're still on Earth. But don't worry, I've got my secret weapon."

"What's that?"

"You."

"Oh. Somehow that's not making me happy. Can't you just zap us down to Earth with that remote thing?"

He rubbed at his temples. "Yeah, I haven't got a remote, though I really should. I need you on that ship. That's why I made them move the Tardis. I'm sorry, but you've got to go outside."

There was a slight shake in her voice. "But there's Sonteruns out there."

"Sontarans. But they'll all be on battle stations right now. They don't exactly walk about having coffee. I can talk you through it."

"But what if they find me?"

Hearing her friend's anxiousness, Eris grabbed the phone.

"I'm sorry, Donna, if there was any other way then we'd do it."

"The whole planet is choking, Donna."

She paused for a moment, and then -

"What do you need me to do?"

"The Sontarans are inside the factory which means they've got a teleport link with the ship, but they'll have deadlocked it. I need you to reopen the link."

"But I can't even mend a fuse."

"Donna, stop talking about yourself like that. You can do this. I promise."

The duo waited as the faint sound of the Tardis door opening reached them. Then, it squeaked shut again.

"There's a Sonterun. Sontaran."

Eris swore. "Did he see you?"

"No, he's got his back to me."

The Doctor sighed, relieved. "Right, Donna, listen. On the back of his neck, on his collar there's a sort of plug, like a hole. The Probic vent. One blow to the Probic vent knocks them out."

"But he's going to kill me."

"I'm sorry. I swear I'm so sorry, but you've got to try."

Donna took a deep breath, and picked up the mallet from underneath the Tardis console. She opened the door again, taking care to avoid creaking. It was still standing there, facing the other end of the corridor. Taking the mallet in both hands, she swung - and landed a hefty whack directly over the vent. It dropped to the floor like a sack of potatoes, and lay still. She lifted the phone to her ear again.

"Back of the neck."

Eris cheered. "Oh, Donna you're incredible!"

The Doctor, also grinning, reminded them both that she wasn't out of the woods just yet.

"Now then, you got to find the external junction feed to the teleport."

"What, what's it look like?"

"A circular panel on the wall. Big symbol on the front, like a, like a letter T with a horizontal line through it. Or, or, two Fs back to back."

"Oh. Well, there's a door."

"Should be a switch by the side."

"Yeah there is. But it's Sontaran shaped, you need three fingers."

He rolled his eyes automatically. "You've got three fingers."

"Oh, yeah." There was a slight hiss. "I'm through."

"Oh, you are brilliant, you are."

"Shut up. Right. T with a line through it."
A slight commotion from the main area caught their attention, and Eris groaned.

"Sorry Donna, we've got to go. Keep the line open."

The Colonel had clearly come up with another half-cocked idea for getting all his soldiers killed.

"Counterattack."

The Doctor groaned. "I said, you don't stand a chance."

"Positions. That means everyone." He tossed a gas mask at each of them, and led them to the door. Martha's clone grabbed at the Doctor's sleeve.

"You're not going without me."

Eris shot her a look. "Wouldn't dream of it."

Mace took them out to the industrial estate, showing them racks of weapons.

"Latest firing stock. What do you think, Doctor?"

He had been far more interested in pulling the gas mask over his head, throwing his hair into an even wilder state of chaos than usual.

"Are you my mummy?"
Eris snorted, partly at the throwback and partly at the way she imagined Mace would look under his own mask.

"If you could concentrate. Bullets with a rad-steel coating. No copper surface. Should overcome the cordolaine signal."

"But the Sontarans have got lasers. You can't even see in this fog. The night vision doesn't work."

"Thank you, Doctor. Thank you for your lack of faith. But this time, I'm not listening." He pulled off his mask and raised his voice so everyone in the immediate vicinity could hear him. "Attention, all troops. The Sontarans might think of us as primitive, as does every passing species with an axe to grind. They make a mockery of our weapons, our soldiers, our ideals. But no more. From this point on, it stops. From this point on, the people of Earth fight back, and we show them. We show the warriors of Sontar what the human race can do. Trap One to Hawk Major. Go, go, go."

There was a sudden, massive downdraft, blowing the heavy gas away and leaving a circular area relatively clear.

"It's working. The area's clearing. Engines to maximum."

As things cleared, the shape of a familiar vessel in the sky became visible. Eris felt her heart stutter in her throat.

"It's the Valiant."

"UNIT Carrier Ship Valiant reporting for duty. With engines strong enough to clear away the fog."

People started removing their gas masks, and Eris and the Doctor did the same. He was, begrudgingly, impressed.

"Whoa, that's brilliant."

"Getting a taste for it, Doctor?"

"No, not at all. Not me." He had seen the look on his daughter's face, and knew exactly what she was thinking. She'd been shot up there. And the Master's refusal to regenerate had hurt them both. He reached out, and she moved to hang onto his arm. Seeing the interaction - and remembering what he'd read in the files - Mace decided to give them a moment and continue with the operation.

"Valiant, fire at will."

Six acid-green beams from the Valiant shot and converged, forming one thick shot that slammed into the ATMOS factory. As soldiers armed with rocket launchers and steel bullets broke through the loading bay doors, it was clear that the battle was shifting in the humans' favour.

As the Colonel set off, the Doctor remembered that the phone call he had started was still active, and he put the phone to his ear.

"Donna, hold on. I'm coming."

Martha's clone stared after them as they started to move.

"Shouldn't we follow the Colonel?"

Eris patted her on the shoulder, grinning widely to hide her discomfort around the obvious facsimile.

"Nah, where's the fun in that? Just the three of us, Martha Jones. Just like old times."

While they worked their way through the building, the Doctor stopping to scan things at various points, Martha stopped another two attempts at nuclear strikes. Reaching the bottom of the compound, he scanned again.

"Alien technology, this-a way!"

The corridor lights flicked on as they made their way towards the door at the end.

"No Sontarans down here. They can't resist a battle. Here we go."

And they burst into the clone lab.

Eris rushed over to the real Martha, running her hands over the straps that secured her and checking for a pulse.

"Oh, Martha, I'm so sorry. She's still alive."

A clicking sound from behind indicated that the fake Martha had pulled out a gun.

The Doctor turned, eyebrows raised. "Am I supposed to be impressed?"

"Wish you carried a gun now?"

"Not at all."

"I've been stopping the nuclear launch all this time."

"Doing exactly what I wanted. I needed to stop the missiles, just as much as the Sontarans. I'm not having Earth start an interstellar war. You're a triple agent."

"When did you know?"

"About you? Oh, right from the start. Reduced iris contraction, slight thinning of the hair follicles on the left temple. And, frankly, you smell."

Eris wrinkled her nose. "Even I noticed the smell. I'm surprised none of the humans did, you Sontarans really need to make your process less obvious."

He continued as she started deactivating the loop around Martha's head. "You might as well have worn a T shirt saying clone. Although, maybe not in front of Captain Jack. You remember him, don't you? Because you've got all her memories. That's why the Sontarans had to protect her, to keep you inside UNIT. Martha Jones is keeping you alive."

She pried the device off her head, and Martha shot upright, gasping. The clone dropped to the floor, and the Doctor kicked the gun away from it's hand. Just in case.

"It's all right, it's all right, I'm here, I'm here. I've got you, I've got you."

"There was this thing, Doctor, this alien, with this head."

There was a buzz from the phone, and he groaned.

"Oh! Blimey, I'm busy." He tucked it into the crook of his neck. "Got it?"

Donna hissed back. "Yes. Now hurry up."

"Take off the covering. All the blue switches inside, flick them up like a fuse box, and that should get the teleport working."

Half listening to the conversation, Martha set eyes on the slumped figure in the corner.

"Oh, my God. That's me."

The Doctor put his coat around Martha's shoulders and darted off to work on the teleport pod, leaving Eris to help her move over to speak with the clone. It - she - shied away when they got closer.

"Don't touch me."

"It's not my fault. The Sontarans created you, but you had all my memories."

"You've got a brother, sister, mother and father."

"If you don't help me, they're going to die."

"You love them."

"Yes. Remember that?"
Aware that the clone probably didn't have long to live, Eris spoke gently, trying to coax an answer from her.

"The gas. Can you tell us about the gas?"

"You're the enemy!"

The real Martha took her hands. "Then tell me. It's not just poison, what's it for? Martha, please."

She took a shaky breath. "Caesofine concentrate. It's one part of Bosteen, two parts Probic five."

Popping his head up from the teleport controls, the Doctor shouted.

"Clonefeed. It's clonefeed!"

"What's clonefeed?"

"Like amniotic fluid for Sontarans. That's why they're not invading. They're converting the atmosphere, changing the planet into a clone world. Earth becomes a great big hatchery. Because the Sontarans are clones, that's how they reproduce. Give them a planet this big, they'll create billions of new soldiers. The gas isn't poison, it's food."

The clone winced.

"My heart. It's getting slower."

Eris frowned. "I'm sorry. There's nothing we can do."

"In your mind, Martha, you've got so many plans. There's so much that you want to do."

She managed a slight smile. "And I will. Never do tomorrow what you can do today, my mum says, because-"

"Because you never know how long you've got. Martha Jones. All that life."
And with a last stuttering breath, the clone faded away.

SIlently, she slipped her engagement ring from the clone's finger and returned it to her own, and let Eris help her stand upright.

Onboard the Sontaran ship, Donna suddenly found herself in a rather sticky situation.

"Doctor. Blue switches done, but they've found me."

"Now!"

He zapped the teleport with the sonic, and Donna appeared in the pod, breathing heavily and looking irritated.

"Have I ever told you how much I hate you?"

"Hold on, hold on. Get off me, get off me. Got to bring the Tardis down."

He zapped it again, bringing the Tardis back down to where he'd parked it.

"Right, now. Martha, you coming?"

She looked down at the phone she'd taken off her copy.

"What about this nuclear launch thing?"

"Just keep pressing N. We want to keep those missiles on the ground."

The slumped figure in the corner caught Donna's attention, and once she realised what it was she couldn't stop staring. "There's two of them."

Eris pulled her into a quick hug. "Yeah, it's a bit of a long story, I'll explain later. Are you okay?"

"Yeah, just about."

The Doctor pulled them all into the teleport pod.

"Yeah, long story. Here we go. The old team, back together. Well, the new team."

He pointed the sonic at the controls, and Donna's eyes widened.

"We're not going back on that ship!"

"No, no, no. No. I needed to get the teleport working so that we could get to…"

And they appeared in a large recreation area. "Here. The Rattigan Academy, owned by-"

Luke stormed into the room, red in the face and holding his gun in both hands.

"Don't tell anyone what I did. It wasn't my fault, the Sontarans lied to me, they-"

He snatched the gun away from the boy. "If I see one more gun…"

Ignoring the teenager, the women followed the Doctor to the lab. Donna looked Martha up and down with a smirk.

"You know, that coat sort of works."

She grinned. "I feel like a kid in my dad's clothes."

"Oh well, if you're calling him dad, you're definitely getting over him."

That made all three of them crack up, and the slightly bewildered look he shot at them only made it funnier.

Brushing off the distraction, he started picking through the scattered gadgets on the workbenches.

"That's why the Sontarans had to stop the missiles. They were holding back. Because caesofine gas is volatile, that's why they had to use you to stop the nuclear attack. Ground to air engagement could spark off the whole thing."

Martha raised an eyebrow. "What, like set fire to the atmosphere?"

"Yeah. They need all the gas intact to breed their clone army. And all the time we had Luke here in his dream factory. Planning a little trip, were we?"

Luke sniffled. "They promised me a new world."

"You were building equipment, ready to terraform El Mondo Luko so that humans could live there and breathe the air with this. An atmospheric converter."

It was a long grey tube set into a sturdy base, with a small control panel attached by a thick lead. The group took it outside, and as he faffed about with some of the settings, the others looked out at the city.

"That's London. You can't even see it. My family's in there."

"If I can get this on the right setting."

"Doctor, hold on. You said the atmosphere would ignite."

"Yeah, I did, didn't I?"

And he activated the converter. A golden energy pulse flew upwards, vanishing among the murky clouds. There was a moment where nothing happened, and he crossed his fingers, muttering to himself.

"Please, please, please, please, please, please, please."

Then came a low thud, followed by a wave of increasingly loud crackling sounds. They watched as a sheet of fire unfurled across the sky, wrapping itself around the heavy smog and smothering it entirely. As the fire began to burn itself out, shreds of blue sky came into view, and they cheered.

Luke's jaw was practically on the floor. "He's a genius."

Martha nodded, grinning. "Just brilliant."

But the Doctor wasn't so jubilant. "Now we're in trouble."

He carried the converter back into the house and set it down in the teleport pod before turning back to his friends.

"Right. So, Donna, thank you for everything. Martha, you too. Oh, so many times. Eris, you're incredible. Don't ever forget that. Luke, do something clever with your life."

Donna realised exactly what he was doing. "You're saying goodbye."

"Sontarans are never defeated. They'll be getting ready for war. And, well, you know, I've recalibrated this for Sontaran air, so…"

He trailed off, and Martha realised why. "You're going to ignite them."

Donna gasped. "You'll kill yourself!"

"Just send that thing up on it's own. I don't know. Put it on a delay."

Eris was quiet when she spoke. "He can't."

"Why not?"

He nodded. "I've got to give them a choice."

Seeing the look on his daughter's face, he moved to hug her, aware that this may well be the last time he got the chance to do so. He reached her, holding her tight. And then he dropped to the floor. As the others ducked to help, Eris shook the tension out of her fingers and stepped into the pod

"What did you do to him?"
"Little trick he taught me decades back, just a bit of Venusian Aikido. He'll be fine when he wakes up, don't worry. I don't know what his plan was once he got up there, but I've got a solid plan to get out. I can't let him go up there without a guarantee of safety."
"There's no guarantee you'll be safe either." Luke stared at her, unable to comprehend why she was doing it.

"No. But I think I've got a higher chance of getting out than he does. Tell him… tell him I'm sorry. I'll see you on the other side."

And she activated the teleport.

She flashed into view on the teleport pad in the control deck, and Staal sneered up at her.

"Oh, excellent. One of the Doctor's footsoldiers, come to act as sacrifice."

"General Staal, you know what this is. But there's one more option. You can go. Just leave. Sontaran High Command need never know what happened here."

"Your stratagem would be wise if Sontarans feared death, but we do not. At arms."

"Staal, I'll do it. If it saves the Earth, I'll do it."

"A warrior doesn't talk, she acts."

"I am giving you the chance to leave. The chance to fight another day, somewhere else in the universe."

"And miss the glory of this moment? The Doctor will be broken either way - he shall lose the planet he adores, or he shall lose one of his dearest friends."

He regained consciousness with a gasp, almost smacking heads with Martha as he jolted upright. He looked around. Donna was on his left, Martha on his right, and Luke Rattigan was kneeling by the teleport pod, looking dazed and afraid.

"Where's Eris?"

He knew the answer already - he just wanted to hear someone else say it.

Martha rubbed his shoulder. "She went up there. She said she had a plan to get out, and she asked us to tell you that she's sorry."

"Oh, she will be sorry. If she gets out of there alive."

The bitterness in his tone was a shock to them all, although Donna could understand his concern.

"Surely she… I mean, if you didn't think you were going to get out, what chance does she have?"

"A higher chance than a normal human, but a lower chance than me. I've told her before not to put herself at risk in situations she doesn't understand, but she never listens!"

He was clearly angry, and Martha tried to offer a sliver of reassurance.

"She took the sonic, and she's not stupid."

"Going up there was stupid. It's a decision she'll regret if she makes it back."

"I'm warning you." She could hear the steel slipping from her voice, but refused to back down. This was the only way to do things.

"And I salute you. Take aim."

The surrounding Sontarans lifted their weapons, and she felt her heart skip.

"If you shoot me, I'm still going to press this. You'll die, Staal. There's nothing you can do about it."

"Knowing that you die too. For the glory of Sontar. Sontar-ha. Sontar-ha. Sontar-ha."

The chanting continued, and she raised the controls threateningly.

"I'll do it."

"Then do it!"

She hesitated, and one of the Sontarans started a countdown over the speakers, indicating the pattern of attack on the planet below.

"Ten, nine, eight, seven-"

She shifted on the spot, pressing the tip of the sonic screwdriver into the side of the control box.

"Six, five, four, three-"

She slammed the converter button, activating the sonic and reaching for the teleport controls.

"Two, one."

She vanished just as the converter exploded, feeling a wave of heat against her hands and forearms as she dissipated through space.

Appearing in the pod back on Earth - and crashing into Luke where he was fiddling with the controls - she moved everyone out of the way as it sparked, the connection failing permanently as the central relay was destroyed. Breathless, she looked up at her friends, a relieved smile on most of their faces. Except one. The Doctor's face was stony, and he barely made eye contact with her for a second before turning on his heel and storming out of the room.

A couple of days had passed, in which UNIT had a lot of cleaning up to do. Not that they had any help from the Doctor and his friends with that. Colonel Mace hadn't taken the Brigadier seriously when he'd said that they would slip away like thieves in the night - but he'd been entirely correct. The only thing they had done before leaving was request that Ross Jenkins receive a promotion, which the Brigadier approved within an hour. And Jenkins refused to tell anyone where they had moved on to - although Price had privately theorised to him that part of the reasoning for that was the purplish marks that peeked out from under his collar. Those had appeared not long after Eris had said a last goodbye to everyone before heading off to catch up with the others. The rest of the mess - including setting up some support networks for a now very lost and lonely Luke Rattigan.

Sylvia lugged the shopping bags through the door and dragged them through to the kitchen, oblivious to the fact that her father and daughter had clearly been deep in discussion when she'd entered.

"The streets are half empty. People still aren't driving. There's kids on bikes all over the place. It's wonderful. Unpack that lot, I'm going to see if Suzette's all right."

Wilf tapped the side of his nose. "I won't tell her. Best not. Just keep it as our little secret, eh?"

"Yeah." Donna grinned

"And you go with him, that wonderful Doctor. You go and see the stars, and then bring a bit of them back for your old Gramps."

"Love you lots, Grandad."

The tension in the ship was palpable when she entered, and the look of relief on Martha's face told her that it had been like that a while. The Doctor and Eris were standing on opposite sides of the control room, refusing to even look at each other. She doubted they'd actually said a word to each other since she'd returned from the Sontaran ship.

"How were they?"

"Oh, same old stuff. They're fine. So, you going to come with us? We're not exactly short of space."

Martha smiled fondly, patted the console, and stepped away. "Oh, I have missed all this, but, you know. I'm good here, back at home. And I'm better for having been away. Besides, someone needs me. Never mind the universe, I've got a great big world of my own now."

She was cut off by the doors slamming shut of their own accord. Seconds passed, and the time rotor activated, tossing them to the floor as the turbulence struck. The Doctor clawed his way to the console.

"What? What?"

"Doctor, don't you dare!"

"No, no, no. I didn't touch anything. We're in flight. It's not me."

Donna clung to the railings. "Where are we going?"

Stumbling, Eris managed to make her way over and ducked under the console, fiddling with whatever she could get her hands on.

"I don't know. It's out of control!"

Arms wrapped around one of the buttresses, Martha glared at her friends.

"Doctor, just listen to me. Eris, you take me home. Take me home right now! Now!"

But there was nothing they could do - the ship had taken charge. And they had no idea how to stop it.

AN: Hello, dear friends! I hope you enjoyed this chapter (I really enjoyed writing it) and I hope you're looking forward to the rest of the story. Now, just as a reminder, I'm alternating uploads between this series and my new one, Vaster Than Empires. So the next chapter I post will be chapter 3 of Crossfade, Evolution of the Daleks.

See you soon, and happy reading!

Much love, Azzie xx