The Doctor ran across the console room floor as the mauve alert flashed its lurid colour. Rose sighed. She'd hoped for a quiet evening. She wasn't sure if he realised, but today, by her watch, was the fifth anniversary of the day they first met, March 4th, 2005. Of course, they were in temporal orbit and time was meaningless, and they could just as easily land a hundred thousand years before or after that date, or twelve months later like the first time. But by the watch that kept her in touch with real time, it was March 4th, 2010 now and they had been knocking about together for five years. She hoped he DID realise. Strangely, for a Time Lord, he was appallingly bad at remembering personal dates in his own life. She wasn't even entirely sure when his birthday was. He seemed to announce it roughly once every twelve months and take her somewhere special to celebrate. She doubted he would have remembered this date. But she REALLY hoped he would, because she would NEVER forget it.

"So what's the Mauve alert?" she asked. "And where and when?"

"London, March 2010," he said. "Oh! Fantastic!" He grinned his familiar devilishly mischievous grin, first at Rose and then at Wyn who hovered nearby listening to their banter. "Wyn, you've never been to 10 Downing Street have you?"

"No," she said. "Been to the Welsh Assembly building on a school tour. Dead boring. Seen the pictures of Downing Street though. Before and after. They rebuilt it nearly exactly as it was before the gas explosion in 2006."

The Doctor laughed. So did Rose. Wyn looked at them both.

"What?"

"Do people REALLY believe the gas explosion story?" The Doctor asked. "Honestly, you Humans. Sometimes you can be so thick."

"It wasn't a gas explosion," Rose said. "Aliens tried to nuke the Earth and make it into radioactive fuel."

"No," Wyn protested. "The alien ship was a hoax. It was a test to see if the emergency services could respond to a crisis. The damage to Big Ben was accidental. The thing went off course. There's no such thing as aliens."

The Doctor decided this was a good time to check the wiring underneath the life-support console. Wyn looked at him and light dawned.

"What am I talking about? HE'S an alien! I keep forgetting. All the time I've been in the TARDIS I still expect aliens to be green bug-eyed things. It really WAS an alien attack? Aliens blew up 10 Downing Street?"

"Yeah." The Doctor barely suppressed his laughter. "Only it was THIS alien that did it to kill the green bug eyed monsters inside the building."

"Actually, it was Mickey who did the blowing up," Rose reminded him. "You just talked him through it. And let's not forget we were IN the building at the time."

"Ok, I give up," Wyn said. "I've been lied to by my government. What's new there? So what about 10 Downing Street anyway? And why is that purple thing flashing?"

"We're on our way there now," The Doctor said. "The purple thing is a mauve alert. That means something dangerous is happening. And they need me."

"Harriet sent it," Rose added.

"Harriet… as in Harriet Jones, the Prime Minister?"

"She's the only one with the subspace code."

"What kind of danger?" Wyn asked. "More aliens? And how long have you two been on first name terms with the Prime Minister?"

"Well, when you've all been blown up together it kind of brings you close," The Doctor said.

"Can't be aliens," Rose observed. "Rassilon's Envelope protects Earth from attack now."

"Hah!" The Doctor answered. "We know better than that. He meant well, old Rassilon, but the Envelope is more trouble than it's worth sometimes. It would be nice to have some idea of what's going on before we arrive though, wouldn't it."

"I wish I knew what you two were talking about to begin with. Subspace codes and envelopes…. Are you sure Rose is from Earth? She talks like you do, Doctor!"

"Oh, she is," The Doctor assured her. "My chirpy little cockney sparrow. We've been together so long now, here in this old box of mine. She's learnt to be a bone-fide time traveller, not just a hitchhiker."

"Wonder how long it would take me to do that," Wyn said. "But I suppose you wouldn't let me stay that long. You didn't REALLY want me in the first place."

"Wyn," The Doctor sighed. "The number of people I've actually ASKED to join me here in the TARDIS, on this strange endless journey of mine, you could count on one hand, even including Grace who said no. Most everybody else strayed in by accident, fell through the door, got lost, stowed away, thought it was a real police box. But sooner or later they all grew on me. You could stay forever as far as I'm concerned. But your mum will want you back one of these days."

"You really mean that?" Wyn asked. "Does that mean you like me?"

"Course I like you," he said.

"But you're always threatening to put me in the airlock."

"Well, there you go. If I didn't like you I wouldn't just threaten it. Goodness knows, there have been times when EVERYONE I've travelled with has driven me so nuts I wanted to try out a cruel or unusual punishment on them."

"What, even my mum?" Wyn asked.

"Oh yes!"

"Or me?" Rose said.

"Specially you." But he said that with one of his extra wide grins that she knew so well before he returned to fine tuning the TARDIS co-ordinates to land in 10 Downing Street without setting off any security alerts. He was rather surprised when Wyn came to him and hugged him. She didn't say why, and afterwards she backed off quickly as if to imply that she would NEVER do anything so girlish and it had all been some kind of hallucination on his part. But he knew better. There was more of her mum in Wyn than she would let on.

They materialised in the main hall inside the reconstructed front door. As he stepped out The Doctor was surprised by the way it had been so faithfully rebuilt as it used to look before he helped to blow it up. For a moment he thought he had got his dates wrong and this was BEFORE the explosion. But the appearance of the Prime Minister herself from the drawing room reassured him.

“Harriet Jones,” The Doctor said with a smile. “How are you?”

“I am quite well,” she answered. “But as ever when we meet, the world is in desperate trouble.”

“What is it this time then?” he asked. “And how can I help?”

“You already have, by being here. I feel as if we have a chance now.”

“Kind of you to say so, Harriet, but you surely didn’t just bring me here for moral support?”

“Of course not. Let me bring you to the emergency situation room.” She looked around at Rose and Wyn. “They’ll make a fuss about security, of course. But I AM Prime Minister, so if I say your friends are cleared they will have to take my word for it.”

"Well, that makes a change," Rose muttered as they followed the Prime Minister along a series of corridors and down stairwells to the basement of Downing Street.

"The nuclear bunker," Harriet said almost apologetically. "It seems wrong to me. I'm the leader of this country - I'm like the captain of the ship - but I'm not allowed to go down with the country. I have to come here and wait it out while everyone else dies. I think there is something very wrong with that idea. I really do."

"As long as you keep thinking that way, Harriet, you've got my vote."

"Doctor, are you even REGISTERED to vote?"

"I'm not, technically, a British citizen," he admitted. "So no. But if I was, I'd vote for you."

"Good heavens. I never even thought of it like that." Harriet exclaimed. "But you're an alien…." She laughed ironically. "An illegal alien!"

"Yep."

"I looked you up, Doctor. When I was elected and all the classified files were opened to me. I found you in the system. You've been looking after this country - this world - for so long. And yet you don't even have the ACTUAL right to live in this country."

"I've got free parking," he said. Rose laughed. That was the last laugh for a while, though. They reached the situation room. They sat around the table facing a wall mounted video screen. A man dressed in the uniform of a U.N.I.T. Major stepped up and set the video running and turned to face them.

"Fourteen days ago the ESA unmanned probe Merlin 6 returned to Earth as scheduled. It soft landed in the sea just inside the Irish Box. We retrieved the probe with the assistance of the Irish Navy and brought it to U.N.I.T. HQ's secure research centre in London." On screen pictures of the retrieval of a space capsule from the sea were followed up by pictures of a helicopter landing on the roof of the Tower of London and then scientists opening the probe. The Major looked at the Prime Minister uncertainly and froze the picture.

"Excuse me, ma'am, I know it's a little late to ask, but are these people actually cleared? I've just revealed that our secure HQ is underneath the Tower of London…"

"Major Wright, 'These people' as you call them have kept more of our secrets than you can begin to imagine," Harriet answered. "THIS is The Doctor. And these are….well, they are with him. And that's good enough for me."

"The Doctor?" Wright looked at him. He grinned disarmingly and waved. Rose and Wyn both looked at each other. Neither were entirely happy about being simply 'with him'. But for the moment that was their role. The Doctor's cheerleader section, his 'moral support'.

"Yes," Harriet told him. "The Doctor."

"Yes," Wright said. "I know who he is. But I never expected…."

"Yes, we all know the legend," Harriet cut him off. "Really Major, I would have thought better of you. Let's leave the autographed photos until we've saved the world."

"I quite agree," The Doctor said. "Please carry on, Major."

"The probe was sent out fifteen years ago to collect possible plant or animal life in the far reaches of the solar system. When it was opened, our scientists found what they believed to be a form of life unknown to Humanity." The Doctor sat up very straight as he saw the images on screen. They showed a molecular model of the 'new life'.

"Organic crystal - living, growing plant-life with a crystalline molecular structure." The Doctor said.

"Yes. Exactly. Well, you can imagine how exciting this was. We immediately brought in all the best people to work on what we found. A new form of organic life…."

"New to Earth," The Doctor pointed out. "But there's a big universe out there."

"New to Earth," Wright amended. "New to the Human race. So we conducted experiments…"

The Doctor suppressed a sarcastic laugh there. "New to the Human race… so we conducted experiments…" He remembered being new to Van Statten's interests and the agony he suffered while his molecular structure was being experimented on by the scientists in that bunker in Utah. No wonder this planet got itself into so much trouble, he thought.

How much trouble, he still hadn't found out. He watched the screen and listened to Wright's briefing into how the best scientific minds in Europe had made a ghastly mistake. They had failed to see that the organic crystal, having grown exponentially under laboratory conditions, had developed spore capsules. These burst filling the air in the laboratory with millions of potential new crystalline plants, which began growing wherever they landed. Within minutes every surface in the laboratory was covered with a mauve-coloured vegetation - including the bodies of the scientists.

"Mauve and dangerous," Rose thought. "VERY dangerous."

"The organic crystal works the opposite way to ordinary plant life," Wright explained. "Where plants draw in carbon dioxide from the air and give out oxygen, this alien plant life takes in oxygen and gives out carbon dioxide. This is NOT speeded up film. This happened in real time. The oxygen in the room was depleted and the scientists suffocated."

Everyone watching seemed to pause to consider the horrible implications of what he had told them. Wyn looked especially horrified. Wright looked at her and shook his head. Whatever anyone said, this was no place for a young girl, he thought.

"Three men managed to get out of the room, but the spores were on their clothes - in their hair. In their panic they brought it out of the secure area." The scene changed to show a corridor with mauve vegetation growing in the footprints of the men, leading to where their bodies had finally collapsed. The scene shifted again to show the whole of the Tower of London overwhelmed by the alien vegetation.

"Needless to say the ravens have flown away," Harriet said. The comment seemed frivolous, but even The Doctor knew the legend that England would fall if the Ravens left the Tower of London. Nobody had ever suspected it would happen in such a way, though.

"Never mind the ravens. What about the people?" Wyn spoke up suddenly. "The scientists…."

"They all died," Wright said. "Everyone who knew anything about this kind of thing All the top scientists, military and civilians."

"I would have thought the British government would have learnt their lesson last time when the Slitheen killed all their alien experts," The Doctor said. "What's that old saying about all the eggs in one basket."

"Sorry," Harriet said, though why anyone would have thought it was her fault The Doctor could not imagine. It was as if, as the leader of the country, she took on its every responsibility on her own shoulders.

"Doctor…." Wyn's voice sounded scared and small but it cut Wright off from continuing his briefing. "Doctor… My dad is…. He's one of the top civilian scientists in this country. Is he… was he…." She looked at the ghastly scene on the screen and turned away. The Doctor put his hand on her shoulder and looked at Harriet.

"Well?" he asked. "Was he? Clifford Jones. Was he one of the people you brought in?"

Harriet looked at him then at Wright. He shrugged to indicate he didn't know. Harriet made an impatient sound and went out of the room muttering something about 'if you want a job done properly do it yourself'. Wright tried to continue his briefing but The Doctor stopped him. Until Wyn knew the answer to her question he was not ready to hear any more.

Harriet returned.

"No," she said. "We apparently tried to get Professor Jones, but he's away in Australia. Mrs Jones said he's in the Outback, looking for some kind of fungus that grows on ant-hills or something."

"Oh!" Wyn sighed with relief and hugged Harriet before she realised that she was hugging the Prime Minister. She blushed red and turned to The Doctor and hugged him before her carefully affected 'cool' reasserted itself.

"May we continue?" Wright asked. The Doctor told him he may in a tone that made it quite clear that, contrary to what Wright thought, he was NOT the one in charge.

"We could find no way of stopping the vegetation once it reached the open air - unlimited oxygen. It has been spreading steadily ever since. The emergency services have tried everything. Fire has no affect on it. CO2 foam slows it down. Inhibits it somehow, but it won't kill it. We have every fire appliance in greater London trying to hold it back, but it's only a matter of time."

"It's even reached here," Harriet said. "That's why you were the only person we could call in, Doctor, with your ship. Downing Street was overwhelmed by it early this morning. We are safe inside. And even if the upper floors are affected, this bunker can be secured. But, as I said, that feels too much as if we are abandoning the people to their fate."

"We can get out in the TARDIS," Rose said. "We did that for the American President once when the White House was under threat."

"That's not why you're here," Harriet told her. "We don't want to evacuate. Though the offer is very kind…. We have set up a laboratory. We hoped…. I don't even know if it's your kind of thing, Doctor. You have never told us what SORT of Doctor you are… but…"

"I'm whatever kind of Doctor you want me to be," he said. "And this is exactly my kind of thing." He stood up, suddenly animated and with that bright gleam in his eye that Rose recognised well enough. It meant that he was running on adrenaline and itching for action. "No point hanging about here chin-wagging," he said. "Let's have a look at your lab. Wyn, Rose, I'll need you to assist me."

"What about me?" Harriet asked. "What should I do?"

The Doctor looked at her. Was she really asking him that?

"Tea, please. Milk, two sugars," he said with a warm smile.

"You want ME to make tea?" Harriet looked at him in amazement. "I AM Prime Minister."

"That make you too good to make tea?" The Doctor asked her.

"No, but…"

"It's ok, Harriet, you don't have to do the tea. Doesn't seem like I have time to drink it anyway. Why don't you get on TV. Reassure the people of Britain. Be the one they can trust in. That's all they've ever wanted from you or any politician."

The makeshift laboratory in the basement of No. 10 Downing Street had everything he would need. Samples of the vegetation were in sealed containers, and a U.N.I.T. man in a white lab coat introduced himself as Kerrigan and told him he was there to assist him.

"I think I have all the help I need," The Doctor said as he began to set up slide cultures of the vegetation inside an enclosed incubator that kept the deadly material separated from him. He set Rose and Wyn at their own tasks as he worked. Rose was preparing more slides as if she had done it every day of her life. Wyn was examining them under the electron microscope.

"These girls?" Kerrigan looked at them scathingly. Rose felt as if she could read his thoughts. A bimbo and a kid, was what he was thinking.

"Yes," The Doctor said, catching her thought. "He is. And he's wrong. Kerrigan, you need to learn not to go by first impressions. People are rarely what they seem to be. People think I'm just a bloke in a leather jacket." He turned from the incubator to the computer console and typed faster than the eye could see. His own eyes were painful to watch as he followed the information that poured onto the screen. The pupils dilated rapidly while he remained unblinking far longer than Humanly possible.

"We have twelve hours."

"Until what?" Rose asked.

“Until the vegetation produces spores again. That’s the time we have left in the cycle from immature to mature plant. It takes thirty-six hours. The spores were released in the Tower of London lab twenty four hours ago. We have twelve hours left before the new plants release their spores not into a laboratory underground but into the open air….”

"The wind will blow them…." Rose couldn't finish her sentence. She understood well enough even before The Doctor moved aside from the computer monitor and she saw the estimated model of the affected area. From Greater London the spores could cover the whole of the British Isles and most of the coast of France and Belgium in a few hours.

"And when those plants mature - if nobody has found a way to stop them…" The map slowly panned out from Britain and Europe as the alien vegetation spread across the entire planet. "The end of life as you know it."

"And we're the only ones who can stop it." Rose looked at The Doctor. "YOU are the only one who can save us."

"What's new?" he asked as he returned to the incubator and continued working. "Nothing is indestructible. There must be something that reacts against the molecular structure and breaks it down. Just got to find out what."

"What could do that?" Kerrigan asked. The Doctor looked at him. "This is an alien entity. What on EARTH could react against it?"

"I don't know yet. It could be anything," The Doctor told him. "Anything from common salt to cough medicine. We have to TRY as many things as possible. So take a culture and get cracking. Wyn, you know how to do this kind of thing. Process of elimination…. Rose… Find samples of everything you can think of…"

"Such as what?" she asked.

"Common salt, cough medicine…. ANYTHING," he said.

Rose looked at him and at Wyn who moved alongside him and began testing samples as if she knew what she was doing. She was on the point of objecting to being asked to fetch and carry, but he was right. In this instance, that was all she could do. She ran upstairs, to the kitchen, the cleaning cupboards, the drinks cabinet, who knows, maybe a single malt would kill the mauve invader, even the Prime Minister's bedroom where she grabbed everything from the dressing table and the bathroom.

"But if he says anything patronising like 'good girl' when I get back," she thought. "I'll kick him where it hurts."

He didn't say anything. He was already deeply engrossed in the experiment, testing slide after slide for any kind of reaction, running simulations on the computer. As she dropped the collection of household chemical compounds on the table he handed her a copy of the periodic table and told her to check off Gold, Silver, Magnesium, Lithium, Beryllium and chromium.

"When we're through with the basic elements we'll try compounds," he said. "Some combination of chemicals may be the thing."

"We can do it in twelve hours?" Rose asked.

"We can try," he said. "Scratch Boron, Carbon, Nitrogen, Fluorine, Neon. We have to try. We have to try to the very last possible moment and then beyond that moment. Even if… if we can't save London, if we can't save the British Isles, we keep going for the sake of the planet."

"Scratch tin and iodine," Wyn said. And Kerrigan added Mercury, Manganese, Iron and Cobalt to the list of substances that had no effect on the crystalline vegetation and then added his own personal belief that the whole exercise was stupid and pointless.

"You have any better ideas Kerrigan?" The Doctor asked without looking away from the task. Kerrigan hadn't. "Then let's crack on with the only thing we CAN do," he said. "And let's stop whinging. Wyn, you holding out ok?"

"Wish my dad was here," she said. "He could help."

"Yes, he could," The Doctor told her. "But he's not. And at least be glad that he's safe - for now." His eyes flickered to the computer and he reached and turned off the worst case scenario model that showed Australia and its outback just as badly affected as any other part of Earth. He looked at Wyn and smiled proudly. A long time back her mother, when only a few years older than she was now, had stood beside him in the same way assisting him to fight whatever threat Earth and its people faced. History had a habit of repeating itself in irritating ways. It made a change for it to repeat itself in good ways.

And Rose. She never even passed the General Science GCSE. She had told him that long ago. But she was doing her best. At least she'd be able to go on Mastermind with questions about the periodic table by the time this was over, he reflected.

All they could do was try. And everyone WAS trying. Kerrigan was doing it in an irritating way, moaning and complaining every five minutes that it was hopeless, but even HE was trying. The best thing about Humans was their reluctance to ever admit defeat. It was one of the few things he had in common with them.

And he was not going to be defeated by a plant, no matter what sort.

"Doctor," Wyn asked a question. An intelligent question, a pertinent and relevant one that made perfect sense in the light of the situation. He smiled at her and prepared to answer, but he was cut off by Kerrigan.

"Really, can we not get this kid out of our way? We have serious work to do, not playtime."

Wyn looked hurt. The Doctor was not surprised. And he was not having it.

"THIS is not a KID. This is Miss Blodwyn Grant Jones, daughter of the twice Nobel Prize winner, Professor Clifford Jones and of Josephine Grant, one of the earliest and most courageous U.N.I.T. operatives in the history of your organisation. SHE herself has experiences you could only dream of. She has more courage in her little finger than you'll ever know. And above all, I TRUST her with my life." He stepped back from the workbench. "Miss Jones, please take charge here for a while. There is something I have to do."

"Yes, Doctor" she said and took up position by the incubator and continued his work. The Doctor gave a last hard stare at Kerrigan and walked away. He beckoned to Rose who put down her checklist and followed.

They found Harriet back in the situation room. She had the worried, frustrated look of somebody who wanted to be doing something but for the moment was surplus to requirements.

"The evacuation of London is not working," Harriet said with a deep sigh. "All we've done is created the biggest traffic snarl up since the day congestion charges were abolished. There are millions of people stuck in cars going nowhere. When the spores distribute again….."

The Doctor nodded. She didn't need to go on. He could see it in his mind's eye. People suffocating in their cars as the vegetation crept over them, stealing the oxygen.

"I phoned my mum," Rose said. "She's still in the flat. She couldn't get away at all. Mickey and Linda are with her. They couldn't get away either so they went to her place because they thought maybe, being a high rise - way above ground - it might be safer. But when the spores get airborne it won't, will it?"

"I'm sorry," Harriet told her. Rose looked at her in something like disgust.

"You're SORRY? This is MY MUM and MICKEY. This is HIS girlfriend. SHE is pregnant. Mum and Mickey were the ones that saved everyone's skin the last time… when the Slitheen were here. Have you forgotten that?"

"Of course I haven't," the Prime Minister replied. "I understand your feelings. But where do we draw the line? Your mother, your ex-boyfriend, his girlfriend, HIS mother? Her sister… If we flew in a helicopter to take them to safety, what about everyone else in the flats they live in? What about everyone else in London?"

"Who needs a helicopter?" The Doctor said. "Come on Rose, let's go get our family. Harriet, we'll be back."

Jackie was trying to take precautions as the TV advised. She'd locked and secured the windows and filled as many bottles as she could with water and then turned off the supply at the stop cock. She'd put towels and rags against the front door and the door to the balcony where the draughts always came in. The flat was secure. But they were stuck in it with nothing but a repeated message on the TV to stay calm. It wasn't helping. She didn't feel calm.

Talking to Rose had helped. She was glad to hear she was safe. In 10 Downing Street of all places. And that The Doctor was there, doing what he could. She knew Humanity's chances of getting through this new threat were much better with him around. But she wasn't sure she'd be alive by the time it was over.

At least Rose was safe. The Doctor would look after her.

She almost screamed when she heard the familiar sound of the TARDIS materialising in the kitchen. She ran through and watched as the insubstantial shape became substantial and real. The moment the sound died away the door opened and Rose rushed out, followed by The Doctor. While she was busy hugging her daughter Mickey hovered in the doorway. Behind him, startled by the new developments, was Linda.

"Come on, Mickey," The Doctor said. "I'm getting you out of here."

"Getting out how?" Linda asked.

"In the TARDIS?" Mickey took hold of his girlfriend's hand.

"In the TARDIS," The Doctor told him with a grin.

"Is it safe for Linda?" Mickey asked. "She's pregnant, you know."

The Doctor looked at Linda and noted, not for the first time, Mickey's ability, far more than any other Human he knew, to state the patently obvious. The only way she could be MORE pregnant than she looked right now would be if she had married a Time Lord. She must have been at least eight months. Half way for a Gallifreyan pregnancy, but nearly there for Human.

"It's perfectly safe," The Doctor assured him. "Come on, both of you."

"What is this?" Linda asked as Mickey made her sit down in the TARDIS. "And why does this sofa have the seal of the American President on it? Is this American?"

"Certainly not," The Doctor replied as he set their co-ordinates back to Downing Street. "It's MINE. The TARDIS - MY space and time machine."

"And you are?"

"I'm The Doctor. Did Mickey never tell you about me?"

"No, I didn't," Mickey said. "You're ok, Doctor. I like you. But I wanted a real girlfriend. I didn't want her scared off by me telling her all about the space alien I know who took me to outer space and the bog monsters in London and all that."

The Doctor looked a little hurt at that. Rose went to him.

"You ARE kind of a big thing for us 'stupid apes' to get our heads around, you know," she told him. "Anyway, I LOVE you still."

He smiled at her and kissed her quickly before returning to what he had to do.

"Oh %$£$^"*," he said.

"Still don't know what that means," Rose said. "But it doesn't sound good."

"We overshot. The underground bunker at Downing Street has lead panelling against nuclear radiation - primitive, but because I didn't take it into account the TARDIS bounced off it. We've materialised in the garden of number 10 and…." He switched on the viewscreen. The garden was full of the mauve vegetation and it was creeping up around the TARDIS. The Doctor switched views and they could see its tendrils snaking slowly around the door.

"Well, we can dematerialise again, can't we?" Rose asked. "Have another shot at parking it in the right spot."

"Can't risk it," he said. "The TARDIS is probably already covered in spores. We would contaminate the inside of Downing Street."

"So…."

"So we're quarantined. We stay here. Until it's over."

"What do you mean, over?" Mickey asked.

"I mean over…. Either they find a way to kill the alien vegetation or everything on this planet dies."

"We're trapped in here?" Linda looked around the console room fearfully.

"I'd rather be trapped in here than trapped in the flat," Jackie said. "This is the TARDIS. It's got everything we need to survive."

"Does it have a maternity hospital?" Linda asked.

"Do we need one?" The Doctor looked at her with a worried expression.

"Depends how long we're going to be in here," she said. "You… What sort of a Doctor are you anyway?"

"What sort of Doctor do you need me to be?"

"Are you REALLY an alien?"

"Yes, I am," he admitted.

"But you…." She looked at Rose. "You kissed him."

"I'm engaged to him," Rose said. "I'm allowed."

"No!" Linda protested. "You're…. You're an air hostess. That's what I heard. You're going out with a pilot."

"He's a pilot too. He flies the TARDIS."

"Can we have a bit of hush?" The Doctor asked as he took Rose's mobile phone from the back pocket of her jeans and dialled. "Wyn, how are things going?" Wyn replied to him. "Ok, don't worry. Keep trying. We have a problem here, and I need you to hold the fort there. I'm going to patch the TARDIS computer into the terminal there so I can run simulations but you'll have to do the actual tests." She said something else to him. "Yes, Wyn, you can. I'm fast with computers. But I can't prepare a test culture any quicker than a Human. You've as much chance of finding the solution as I have. Believe me. Believe in yourself." She said something else and he smiled. "That's my girl."

Harriet was still feeling useless. She had made as many broadcasts to the nation as it was possible to make. There was nothing else she could tell people. Nothing she could say to them to make them feel better. Nothing that would make her feel better. And now everyone else in the building had a job to do, even if it was only monitoring how fast the alien vegetation was taking over the City of London. And that was faster than they could evacuate the city. That was the depressing, awful truth. And she could do nothing but stand there in the situation room and watch the traffic camera monitors as they scrolled between familiar places - Downing Street, Trafalgar Square, The Mall, Westminster Bridge - even the river couldn't hold this back. The traffic cams changed rapidly, showing streets choked with cars, and the vegetation encroaching. It wasn't like a tsunami or a fireball or a piroclastic cloud from a volcano. It WAS possible to run from it, and she saw people abandoning their cars to do that. But there was only so far and so long people could run for. If they could not find a way of stopping it, then they were doomed.

Wyn was doing her best. But she did wonder why The Doctor had trusted her. She didn't even LIKE science. He knew that. And yet, she had grown up in a house that was half laboratory. She had learnt more than she thought she had. She was realising now just how much. She understood how to use the computer to build molecular constructions of the alien vegetation and run simulations of what ought to kill it. She knew how to prepare slides of the culture and test one after the other the chemical compounds they hoped would kill it. So far they knew that CO2 foam would slow it down. But it didn't kill it.

The world depended on her. Wyn almost fainted when she realised. The Doctor had left it in her hands. It ALL depended on her. She wasn't her dad. She wasn't even her mum. She was just sixteen, nearly seventeen, with no a-levels, because she had been travelling with the Doctor and hadn't been to school for six months. And the world was going to choke to death unless she could find the answer.

"Doctor… I can't," she whimpered. Then she thought of him when he had stepped back and told her to take over. The look in his eyes. He actually believed in her. It wasn't just to put Kerrigan's nose out of joint. He knew she COULD do it.

"I'll try," she said. "I'll do my best."

"Doctor," Linda looked up from the sofa. The Doctor looked across at her. "You know that maternity hospital…"

"Er…." This was one of those moments when his rudimentary precognition jumped in. His hearts sank. "Oh no…"

"My waters just broke."

"Ok," he said bounding across to her. "Come on, I don't actually have a whole hospital but there's a perfectly adequate medical centre. You'll be fine."

"You know about…. Delivering babies?" Mickey asked. "You've done this before?"

“Oh, only about two hundred and fifty seven times. Mostly Human.”

"Mostly…." Linda looked worried. And she looked in pain.

"Do you mean that most of the babies were Human or that the actual babies were mostly Human…." Mickey's voice trailed off as he realised that the question was utterly irrelevant. The Doctor was ignoring him anyway. He was concerned about Linda.

"I can be any kind of Doctor you want me to be, Linda. You'll be fine." He touched her forehead and radiated calming thoughts. She looked at him as if with new eyes, trusting him implicitly. She let him lift her from the sofa and walk her slowly towards the internal door. "Jackie," he said. "We've been here before, you come along and help. Mickey…" He looked at Mickey. He was standing up but he looked as if he could fall down again any moment. "Rose, you look after Mickey. We'll handle this."

Jackie followed him. Rose took Mickey back to the sofa. He really wasn't handling this very well at all.

"Hey," she said. "She'll be all right. The Doctor is looking after her. He's the best."

"I know. I don't worry about The Doctor. I know he'll do what he can. But…" He looked at the viewscreen. It was almost obscured by the creeping vegetation. "I'm… going to be a dad. But…. But the world is about to end!"

"The Doctor will sort that out, too. If he can."

"You believe he can do anything, don't you."

"Never seen him fail yet." Rose took his hand and held it. He was shaking. "It'll all be ok. And hey…. You're going to be a dad. That's fantastic."

"Except…." He glanced at the viewscreen again.

"If the worst happens," Rose said. "If it really is the end…. The Doctor can… I don't know. We've been to loads of planets where Humans live. He could take us to one. There may be some way he can decontaminate the TARDIS and take us all somewhere we can be safe."

"I don't want to live on another planet. I want everything back to normal. I want my garage and my house. My world. I want my kid to grow up on Earth."

"I want your world, too." Rose said. "I know I've got the whole universe. I've got The Doctor, the TARDIS, I can go anywhere. But I want the Earth to be here when I need it to be. So does The Doctor. He….." She stopped. Something horrible had occurred to her. "Oh… it's 2010. If…. If the world ends today…. If the Earth is destroyed and all the people - what happens to Susan and David and the twins and Sukie in 2210?"

"I don't know. Doesn't it mean there's nowhere for them to live in that time?"

"Oh, I wonder if The Doctor has thought of it? He'll be so upset." She was upset herself. She cared as much as he did for the children. And for Susan and David.

"But… but they ARE there in the future. This time is history to them. So…. So that must mean we win. We must beat this thing and be ok." Mickey's brow furrowed as he tried to reason it out.

"I don't know," Rose said. "I don't think it works that way. The one thing I do know from being with The Doctor - nothing is straightforward. Especially not Time."

"Rose…" Mickey began. He put his arms around her and before she realised he had kissed her. It was a quick kiss, over almost as soon as it began, and afterwards they both felt it wasn't quite what they expected.

"Seems funny," he said. "Doesn't seem like when we used to…"

"Well, it wouldn't. We're not the same now. You love Linda, don't you?"

"Yeah. Like mad. She's the best."

"And I love The Doctor. When he kisses me, it's like fireworks in my head, it's like my feet aren't touching the ground. Because I love him."

"It was never like that with us," he said. "I guess we WEREN'T meant for each other."

"No." she said. "But we'll always be friends. You know that." She put her hand over his and squeezed it. He smiled. "Friends."

"Yeah," he said. "Friends."

"Hey," Jackie ran into the console room. "Mickey, Rose…. Come on…quick." Mickey was up like a shot and racing after Jackie as she ran back to the medical centre. Rose followed a little slower off the mark. When she got there Mickey was sitting beside Linda as she lay on the bed. She was holding a tiny newborn baby.

"It's a boy," The Doctor said with a smile as Rose went to him. He put his arm around her waist. "Six pounds two ounces and perfectly healthy."

"That's great," she said. "Congratulations both of you."

"You were terrific," Jackie said to The Doctor and kissed his cheek.

"Steady, Jackie," he said. "People might get to think you like me." But he was smiling. For a moment, in their happiness, they had all put their terrible situation out of their minds. Even The Doctor. Rose was glad. Because she didn't want him to realise what she had realised. That while he had saved HER family - OUR family as he had said to her - he might have lost his own dearest blood.

"Doctor," Linda called to him and he went to her side. "I just wanted to ask. Would you mind if we named the baby after you. That is… I mean…."

"You don't even know what his name is," Rose laughed. The Doctor grinned.

"One of me is enough in the universe," he said. "But my mother wanted to call me Martin. She was pretty miffed when my dad insisted on a Gallifreyan name."

"Martin it is," Linda smiled. "If…. If we're the last Humans left on Earth…. Well he's the hope for the future isn't he? It means all is not lost after all."

"That's right," The Doctor told her. "He's the hope for us all." He kissed her on the forehead and touched Mickey on the shoulder. "You're what the fight's all about," he said. "You're why I keep on doing it. Never forget that."

Rose's mobile rang. She looked at it. It was Wyn. She automatically passed it to The Doctor.

"Wyn," he said. "How are things?"

"Doctor," he heard Wyn's voice on the other end of the phone. "Things are fine. Things are just great. We're coming to get you. We found the solution. The air force are dropping the stuff all over London. It's killing the vegetation stone dead. And we'll be with you in a minute."

"Fantastic!" he cried, his smile broadening. He ran through to the console room and turned on the viewscreen. Outside U.N.I.T. men were spraying something with a red tinge over the vegetation and it was shrinking back, dissolving as they moved forward. Jackie and Rose followed him. They watched in joy as the TARDIS was de-contaminated. At last The Doctor opened the door. They stepped out into the garden, The Doctor and Rose holding hands as they always did when they went anywhere, then Jackie with Mickey holding Linda as she in turn clutched baby Martin close to her.

As they stepped into the hall of 10 Downing Street, Harriet Jones, Prime Minister greeted them all joyfully. The next moment Wyn rushed in followed by Kerrigan and Major Wright. She grinned triumphantly and took a deep breath.

"Aspartyl-phenylalanine-methyl ester combined with N-Ethyl-phenylazo-naphthylamine and capsicum oleoresin." She said. "That's what kills the mauve invader."

Everyone looked blank except for The Doctor.

"Artificial sweetener and chilli powder dyed with Sudan Red!"

"They were in the things I got from the Downing Street KITCHEN," Rose exclaimed. "Sweetex and a box of chilli."

"Last time it was pickled onions," Jackie said.

"I would never have thought of it in a million years," Kerrigan admitted.

"Then you should get out of the lab and into the kitchen more often," The Doctor told him. "Well done, Wyn, you saved the planet."

"She did?" Wyn turned as she heard a familiar voice and ran to her father as he came down the stairs. "I got the message over the Bush Radio to come back to England - national emergency. Twenty-three hours flight and then the plane was diverted to Birmingham of all places and there was a U.N.I.T. helicopter waiting to bring me to 10 Downing Street. But apparently now I'm here you don't need me."

"Well, one member of the Jones family on the case was enough," The Doctor told him. "Wyn is fantastic. You should be proud of her."

"I always am," he said.

"I seem to belong to the wrong Jones's," Harriet said quietly. "Nobody ever said they were proud of me. Not even my mum. She just asks how come I'm on telly so often these days." She sighed and looked around at Jackie, standing alone, slightly bemused by the fact that she was in the hallway of 10 Downing Street, at Mickey and Linda and the baby, The Doctor, clutching Rose's hand tightly as if he never wanted to let her go, at Professor Jones and his daughter, Kerrigan and Major Wright. "Can I get anyone a coffee?" she asked.

Harriet gave everyone coffee. Later she gave them dinner in the State Dining Room - all but Mickey and Linda and the baby who were taken off to hospital by the same helicopter that brought Clifford to Downing Street. After dinner, The Doctor found an excuse to take Rose away from the crowd. They found themselves in a room known as the White Room, which had faithfully recreated the favourite drawing room of Lady Walpole that was destroyed in the fight with the Slitheen. The Doctor looked at Rose for a long moment then took her in his arms and kissed her in that intense, wonderful way that set her heart on fire and fireworks buzzing around her head and made her feel like her feet had left the ground. "Happy anniversary, My Rose."

"You remembered!" She smiled happily. "The day we first met."

"How could I ever forget that day? Running for my life from a building I had just blown up, and all I could think of was two brown eyes and blonde hair and a hand I had held for a few brief minutes." Wyn wasn't in the room, but he knew if she was there would have been a scornful interjection there. He was getting too 'mushy'. "I am so glad you never took the second piece of advice I gave you."

"The first was 'run'," she said with a smile. "What was the second? It was all kind of frantic at the time."

"Forget me," he said. "Go home and forget you ever saw me."

"Couldn't do that. You're just too unforgettable."

"That's just what I thought," he told her. "Rose Tyler - I will never forget her. If I let her slip away from me I will regret it for the rest of my life."

"Liar," she laughed. "You kept trying to get me off your back."

"Ever hear that old song - "A Man Chases a Girl - Until She Catches Him." He grinned and kissed her again. "I've never been so willingly caught. If it didn't seem that way at first, it was because I still had a lot of things I had to get over before I could trust my hearts to somebody else. But Rose… these five years…. They have been the sweetest five years I've known since…. Since my Julia was alive. I thought when I was with her that I was the luckiest man in the universe. And since knowing you I have felt so again. There isn't a gift I could give you that begins to say how much you mean to me. But…." He pressed a small packet into her hand. She opened it carefully and found a silver medallion for the charm bracelet he gave her two Christmases ago. It had a detailed representation of the Earth engraved on it. She smiled.

"You are the only man I know who really COULD give me the Earth," she said as she let him fix it onto her bracelet. "Here… this is for you."

He opened the box she gave him and blinked back a sentimental tear as he looked at the silver lapel pin with the constellation of Sagittarius engraved on it. The nearest thing she could possibly have found in any Earth jewellers shop to a representation of his home. Gallifrey - when it existed - orbited the star in the middle of the bowstring of Sagittarius. As she pinned it through the old leather of his jacket he was utterly speechless. Five billion languages and at that moment there wasn't a word he could think of that fully and completely expressed how he felt. But 'fantastic' came within a few light years of it.