Piper watched as the creature screamed in pain before grabbing Harriet's hand. She needed to find the Doctor, he was the only one that could stop this. She was surprised when Harriet stopped, pulling her back towards the room. What the hell was she thinking?!

"The emergency protocols are still in there! We need them!"

They ran back to the room but screamed when they saw the alien was free and now chasing them. They ran down the hallway, trying every door they came across, but none would open. Piper turned to see the Doctor standing in a lift, smiling like an idiot. He grinned at her then at the creature who lunged at him. He pressed a button. "See ya," he said as the lift doors closed. This gave Piper the time she needed. She dragged Harriet around another corner only to run into Rose, making all three of them scream.

Piper clutched her chest as she fought to bring her breathing under control. "Jesus Rose," she scolded. Rose's face paled as the alien stopped behind Piper and Harriet. "Umm, Piper-" she tried to warn.

"Where the hell have you been? Don't you think it's a bad time to take a stroll?"

But Rose wasn't listening, she pointed at the creature but Piper for once, she wasn't paying full attention. Rose stepped back in fear, causing her to get a strange look from Harriet. The creature reached a claw behind Piper and for one moment, Rose thought it was going to kill her. Instead, the claw reached out and tapped her on the shoulder. This made Harriet look around, her eyes widening in fear. She moved to stand by Rose. Piper rolled her eyes at them. "Seriously, we need to find the Doctor," she said. The claw tapped her again but she moved her shoulder, thinking it was just someone trying to get her attention. "Sorry, now's not a good time," she said without turning around. The claw tapped her once more. "Look, I've just told you-" she trailed off as she saw what was behind her. She waved shakily to the alien. "Umm, hi."

She stepped back, he face pale. Her eyes darted around the room, trying to look for something, anything, she could use. But there wasn't anything around. She nodded slightly. "Hey, Rose?"

"Yeah?"

"Those shoes you're wearing?"

Rose stared at her in disbelief. They were being chased by monsters and she was taking the time to stop and ask about her shoes?!

"Yeah," she said slowly as the alien moved towards them slowly.

"Are they warm?"

Rose could believe this. Why the hell was she asking questions like this now? But then again, she knew Piper never did anything without a reason.

"Yeah," she answered.

"Are they comfortable?"

"Yeah,"

"Are they fast?"

Rose turned to look at Harriet who shrugged.

"Umm, I dunno."

"Let's find out!"

She grabbed Rose's hand, who in turn, grabbed Harriet's and pulled them into a room. They locked the door behind them before looking around. "Okay, we need a hiding place! Rose, you hide behind the curtain! Harriet, you hide behind the sofa!"

"Where are you gonna hide?" Rose asked.

"In the wardrobe," she grinned. "Where else?"

It was at times like this that Piper reminded Rose of the Doctor. They managed to get in their positions just in time. A second later, the door was ripped apart. They heard footsteps and knew looking for them. "Little human children, where are you?" Sweet little humans, come to me."

Piper looked around frantically for anything that could be used as a weapon. Her eys settled on a fire extinguished that was hanging nearby. As quietly as she could, she crawled to it, carefully checking it was the right one. It was. The creature was still talking as she quickly made sure everything was in position and working. She only had one chance at this. She looked up to see Rose peeking from the curtain, looking at her curiously.

"What are you doing?" Rose mouthed to her.

Piper put her finger to her lips and moved silently around the room. She had to get close enough to it before she could use it against the alien. She froze however, when more of the creatures entered the room. She closed her eyes in thought. Dammit! One was bad enough but now there's more. What the hell are we gonna do? No, no! There's a way out. There's always a way out!

"My brothers."

"Happy hunting?"

How many of them were there?

It's wonderful," the one chasing them answered. "The more you prolong it, the more they stink!"

Piper's eyebrows forrowed in confusion. What was that supposed to mean? The more you prolong it the more you stink? Her eyes widened in realization. It must be their sense of smell! Oh, this was not good!

"Sweat and fear. I can smell an old girl, stale bird with brittle bones." Harriet frowned at this.

"And two ripe youngsters, all hormones and adrenalin. Fresh enough to bend before they snap!"

The curtain Rose was hiding behind was pulled back and Rose screamed. Piper this distraction to get close enough. She used the extinguisher on the alien and as an extra precaution, hit it over the head!

Everyone glance at the door as the Doctor charged in holding his own fire extinguisher. He looked around, eyebrows raised. "Did I miss anything?"

Rose grinned. "Well, you missed Piper spray that thing with her fire extinguished. Of course that was before she used it to whack it over the head with!"

The Doctor looked at Piper incrediously as if to say 'Really?'

"Who the hell are you?" He asked Harriet. Without looking at him, she showed him her I.D.

"Harriet Jones, MP for Flydale North," she answered.

"Nice ta meet you."

She smiled. "Likewise."

The Doctor sprayed them before leading them out of the room. "We need to get to the cabinet room."

"The emergency protocols are in there! They give instructions for aliens."

"Harriet Jones, I like you."

"I think I like you too," she replied.

They ran through the way they came, back into the cabinet room. The Doctor grabbed one of the jars of alcohol and raised it up. He pointed the sonic screwdriver at the jar. Piper panicked as the creatures closed in on them. She looked at the sonic and then at the alcohol. "Stop!" She commanded before the Doctor could say anything. This made the others including the aliens turn to look at her. "One more move and his sonic device will triplicate the flammability of this alcohol. Whoosh, we all go up. So back off!"

She looked at the others who were staring at her like she had the answers to the universe. She was happy when the aliens stepped back.

"Right then, question time. Who exactly are the Slitheen?" The Doctor asked them.

"They're aliens," Harriet interrupted.

"I got that, thanks," he said sarcastically.

"Who are you if not human?"

"Who's not human?"

"He's not human," Rose answered.

"He's not human?" She looked at Rose.

"Can I have a bit of hush?" The Doctor asked.

"Sorry."

"So what's the plan?" He turned to the Slitheen.

"But he's got a Northern accent," Harriet interrupted.

"Lot's of planets have a North," Rose quoted.

"I said hush!" He snapped. "So c'mon, you've got a spaceship hidden in the North Sea. It's transmitting a signal. You've murdered your way to the top of the Government. What for, invasion?"

"Why would we invade this godforsaken rock?"

"Well something's brought the Slitheen race here, what is it?" Piper asked. The Doctor nodded in approval.

"Slitheen race? Slitheen is not our species," they said confused. "Slitheen is our surname. Jocrassa Fel Fotch Pasemeer-Day Slitheen, at your service."

"So your family?" The Doctor said.

"The family business."

The Doctor's head snapped up. "Then you're out to make a profit. How can you do that on a godforsaken rock?"

"Uhhh, excuse me," one asked, turning to Piper. "His device will do what? Triplicate the flammability?"

Piper's eyes widened. "Is that what I said?" She asked nervously.

"You're making that up?"

"Ah well, nice try. Harriet have a drink. I think you're gonna need it." He passed the jar to Harriet who was standing to his right.

"Can you pass it to the left?"

"Sorry," he said, handing the bottle to Rose.

"Thanks," she muttered.

"Now we can end this hunt. With a slaughter."

The Doctor crossed his arms. "Shouldn't we run?" Rose asked. "Fascinating history, Downing Street. 2000years ago this was marshland. In 1730, it was occupied by a Mister Chicken," he chuckled. "He was a nice man. In 1796, this was the cabinet room. If the cabinet was in session and in danger, these were about the four safest walls in the whole of Great Britain. End of lesson." The Doctor opened a small square panel and pushed a button. The doors around them sealed. "Installed in 1991. Three inches of steel lining every wall. "They'll never get in." He smiled. Piper couldn't help but facepalm. "Great," she said sarcastically. "And how do we get out?"

"Ah."

The Doctor dragged the corpse of the man they had been talking to earlier into a cupboard. "What's his name?"

"Who?" Harriet asked.

"This one."

"No idea. I gave him a cup of coffee, spoke to him but I never asked his name," she said sadly.

"Right, what have we got?" Anything?"

"What I don't understand," Rose started. "Is why they killed the Prime Minister but didn't use him as a disguise."

"Too slim. They're big old beasts so they need to fit inside big humans."

"Makes sense, I suppose," Piper said thoughfully. The Doctor stopped what he was doing. His eyes narrowed as he looked at her. "What are you thinking?"

Her eyes narrowed at him. "What makes you think I'm thinking?"

"I know that tone," he said simply. "And I know you. You're smart and you've got your thinking face on. So, what are you thinking?"

She began to pace up and down the room. The others watched her in curiosity. "It doesn't make sense," she muttered.

"What doesn't?" He asked patiently.

She walked over to where Harriet had been sitting and picked up some of the papers. Information flashed through her eyes as she worked it out. "They've killed to get to the top but not for invasion. It's for profit," she muttered.

"So?" Rose questioned.

"So, how can they make profit? They obviously need something but what? Look here," she pointed to one of the papers. "It says something about codes. "

"Couldn't we just launch a bomb at them?" Rose said suddenly.

Piper's eyes widened in realization. "A bomb," she breathed. The others looked at her in confusion. "That's it!"

"What's it?"

"Okay, so for codes like that you would need to have access, right? What if...they're profit isn't on Earth?"

"What do you mean?" The Doctor asked.

"What if...it's not on Earth but the Earth itself?"

The Doctor's jaw dropped in awe at her. "Explain!" He said quickly.

"Okay. Remember on platform 1 with Cassandra?"

They nodded. "Remember how she wanted everyone dead because they were worth something." They did remember. She had done it for money. All in all it wasn't a good time. "Well if a person is worth that much imagine what something like a planet could do for someone. You could use it, you could..."

"Could what?" The Doctor urged her.

"Sell it."

Rose's phone beeped suddenly. "Oh, that's me," she said.

Harriet frowned. "But we're sealed off. How can you get a signal?"

"He zapped it. Super phone."

"Then we can phone for help. You must have contacts."

"Dead downstairs," he said grimly.

"It's Mickey." Rose looked down at her phone. The Doctor rolled his eyes in annoyance.

"Oh, tell your stupid boyfriend we're busy!"

Rose moved to show them a picture of a Slitheen being electrocuted. "Yeah, he's not so stupid now after all."

Rose called Mickey. "Is she okay, no don't put her on, just tell me."

The Doctor moved to grab the phone from her. "Is this Rickey? Don't talk just go to your computer. I may just choke before I say this but Mickey the idiot...but I, er, need you."

Rose smirked.

He hooked the phone up to something so they could all hear it. "Say again."

"It's asking for a password."

"Buffalo. Two F's and one L."

They could hear Jackie talking in the background.

"Repeat the password everytime. Why hit Big Ben?"

"You said to gather alien experts so they could kill them."

"Those lot would have gathered for a weather balloon. You don't need to crash into Big Ben. It's like Piper said, it doesn't make sense."

"If they're hiding, why put the world on red alert?" Rose asked.

"Look at her." Jackie grumbled.

"Oi. At least I'm trying!"

"Well I've got a question of my own. Cause since that man walked into our lives I've been attacked in the streets, I have had creatures from the pit of hell in my own living room and my daughter and her best friend disappear off the face of the Earth!"

The Doctor rolled his eyes. Rose sighed. "I told you what happened."

"I'm talking to him! Cause I've seen this life of yours, Doctor. And maybe you get off on it and you think it's clever and smart, but you tell me. Just answer me this. Are they safe?"

The Doctor said nothing.

"We're fine," Rose said.

"Are they safe? Will they always be safe? Can you promise me that?" The Doctor stared at both girls. "Well, what's the answer?"

"We're in," Mickey said breaking the tension.

Piper watched the Doctor as he explained to Mickey what he had to do. A noise filled the room. The Doctor squinted in concentration.

"What is it?" Mickey asked.

"The Slitheen have a spaceship that's transmitting a signal. Now, shut up. I'm trying to work out what it's saying."

"He'll have to answer one day," Jackie muttered.

"Hush!"

"It's a message," the Doctor said.

"What's it saying?" Piper said.

"I dunno. It's on a loop, keeps repeating." A ringing suddenly cut through. "I said hush!"

"It's not me! Go and see who that is," he said to Jackie.

A moment later, Jackie's screaming could be heard.

"They've found us!"

"Mickey, I need that signal!"

Piper glared at him. "Nevermind the damn signal! Get the hell out of there!" She snapped.

"We can't! It's by the door. Oh, my god. It's unmasking. It's going to kill us!" Mickey said, sounding scared.

"There has to be some way of stopping them. You're the expert, think of something!" Harriet said.

"I'm trying!"

"That's my mother!" Rose said, gulping.

"Right, if we're gonna find their weakness, we need to know where they're from. Which planet. So, judging by their basic shape, that narrows it down to 5,000 planets in travelling distance. What else do we know? Information!" He bent over the table ready to narrow it down.

"They're green," Rose said. Piper rolled her eyes. That was kinda obvious!

"Yep, narrows it down."

"Good sense of smell," Piper said.

"Narrows it down."

"They can smell adrenalin," Rose said.

"Narrows it down,"

"The pig technology," Harriet said.

"Narrows it down."

"The spaceship in the Thames. You said slipstreamengine," Piper said.

"Narrows it down."

"It's getting in!"

"We're on it!" Piper said.

"They hunt like it's a ritual," Rose continued.

"Narrows it down."

"Wait a minute! Did you notice, when they fart, if you'll pardon the word, it doesn't just smell like a fart. It's something else. What is it?"

"Ohh, ohhh bad breath!" Piper and Rose said at the same time.

"That's it!"

The Doctor grinned. "Calcium decay. Now that narrows it down!"

"We're getting there mum!"

"Too late," Mickey told her.

"Calcium phosphate. Organic calcium, Living calcium. Creatures made out of living calcuim. What else, what else? Hyphenated surnames. Yes! That narrows it down to oneplanet! Raxacoricofallapatorius! Get in the kitchen."

"What are you gonna do?Write em a letter?" Mickey bit.

"Calcium, recombined with a compression field. Acetic acid. Vinegar!"

"Just like Hannibal!" Harriet exclaimed.

"Just like Hannibal. Mickey, have you got any vinegar?"

"How should I know?" Mickey asked stupidly.

"It's your kitchen!" Piper snapped.

"Cupboard by the sink. middle shelf," Rose told him.

Jackie snatched the phone from Mickey. "Oh, give it here! What do you need?"

"Anything with vinegar!" The Doctor shouted.

"Gherkins, yea, pickled onions. Pickled eggs."

"You kiss this man?" The Doctor asked Rose.

They waited until the screeching stopped followed by what sounded like something exploding before sighing in relief.

"Hannibal?" Rose questioned.

"Hannibal crossed the alps by dissolving boulders with vinegar."

"Hey, listen to this."

They listened as a man told the people about finding weapons of destruction. Of course it was all lies but no one else knew that. They listened as he begged them to release the codes in order to set of a nuclear strike.

"He's making it up, there's no weapons. No threat, he just invented it."

"I would have thought that was obvious, Doctor! Please try and keep up!" Piper snapped.

The Doctor looked at her shocked at her outburst. He smiled at her softly. He was going to enjoy getting to know her completely, figuring out what made her tick and what set her off. But he knew he had all the time for that. After all, she wasn't going anywhere. Not if he had anything to do with it. Even if Rose decided she wanted to go back, he would make sure Piper stayed, somehow. He wanted her to stay.

"Do you think they'll believe him?"

"Well you did last time," Rose said.

"That's why they did that. They want the world panicking. Cause you lot, you get scared, you lash out."

"They release the codes -"

"And the Slitheen go nuclear," the Doctor finished.

"But why?!"

The Doctor pressed the button, raising the steel walls.

"You get the codes, release the missiles but not into space cause there's nothing there. You attack, they retaliate, fight back. World war 3, the planet gets nucked."

"And we can sit through it in our spaceship. Not crashed, just parked. We'll be safe and sound." The female said.

"But you'll destroy the planet, this beautiful place. Whatever for?"

"Profit," the Doctor answered. " That's the signal. It's an advert beaming into space."

"Sale of the century. Reduce the Earth to molten slag and sell it piece by piece. Radioactive chunks capable of powering every cut-price star liner and cargo ship. There's a recession out there, Doctor. People are buying cheap. This rock becomes raw fuel."

"At the cost of five billion lives." The Doctor said.

"Bargain!"

"Then I give you a choice. Leave this planet or I'll stop you," he said coldly.

The Slitheen started laughing. "What, you?...Trapped in your box?"

"Yes. Me," his expression didn't change as he shut the doors in her face.

"Alright, I'm not saying I trust you but there must be something you can do!"

"Mickey, any luck?" Rose called.

"A load of emergency numbers. All on voicemail."

The Doctor and Piper stood leaning against a wall, looking grim.

"If we could just get out of here," Rose said.

"There's a way out," Piper said quietly. Rose and Harriet turned to look at her. "There's always been a way out."

"Well why haven't we used it?" They asked her.

He leaned towards the phone. "Because I can't guarantee that they will be safe."

"Don't you dare. Whatever it is, don't you dare!"

"And if I don't dare, everyone dies."

Rose and Piper glanced at each other, a silent conversation taking place. They nodded to each other before looking at the doctor.

"Do it," Piper commanded.

"You don't even know yet you'll let me do it?"

"Yeah," Rose said.

"Please, they're just kids," Jackie begged.

"Don't you think I know that? This is my life, it's not smart or cleaver, it's standing up and fighting for what's right when no one else will."

"What are you waiting for?"

"I could save the world but lose the both of you."

"Except it's not your choice. It's mine."

"Who the hell are you?" Jackie snapped.

"Harriet Jones, the only elected representative in the room. And on behalf of the people I command you. Do it!"

The Doctor smiled.

"So how do we get out?" Rose asked him.

"We don't. We need to stay here. Use the buffalo password. It overrides everything," he told Mickey. "We need to select a missile."

"But we can't. We haven't got the codes."

"We don't need it. All we need is an ordinary missile. What's the first category?"

"Sub harpoon, UGM-84A."

"That's the one, select. You ready?"

"Yeah."

"Mickey the idiot. The world is in your hands. Fire"

"How solid are these exactly?" Harriet asked, pointing to the walls.

"Not solid enough. They're not built for something this big," he answered.

Rose looked at Piper guiltily. "Sorry," she mouthed to her. Piper looked at her in confusion, wondering what she meant. She found out a moment later.

"We don't necessarily have to die ya know."

The Doctor looked at her, confused. "Well what would you suggest then?"

Rose looked at Piper again. The Doctor caught this and also turned to look at her.

"No," Piper whispered.

"Piper, please. I know you can do this!" Rose pleaded.

"I can't!"

Rose moved to hold onto her arms. "Yes, you can. I know you can. You can save us!"

The Doctor looked from Rose to Piper then back to Rose. "What are you talking about?"

Rose turned to face him. "Would now be a bad time to tell you bout Piper's powers?"

"Powers?"

"Yeah, she had these powers."

He looked at Piper who was looking at anything but them. He closed his eyes in pain. He really didn't want to risk her but if she could save them then he had to at least try. "How powerful is she? What can she do?"

"She can moved objects with her mind, create shields around her and others and other things," Rose answered.

The Doctor turned to Piper. "Can you create a shield around us?" He asked urgently. She nodded.

"I can do better than that." They watched in awe as she raised her hands in the air, a blue shield surrounded them. It covered the room.

She turned to them. "Hide in the cupboared for extra protection."

They nodded. The Doctor stopped when she didn't follow. She shook her head. "I need to stay here to keep the shields up. Go!"

The Doctor was conflicted. He made sure Rose and Harriet were safely inside before standing beside his companion. "I'm not going anywhere. Not without you."

She smiled at him. He smiled back. He watched as she closed her eyes in concentration. The shield around them seemed to glow brighter with every passing moment. He didn't know she had powers but now that he did, he was interested to see what else she could do. Moment later the explosion hit. The room shook violently but Piper was able to use her powers to keep her and the Doctor in place AND keep the shields up. As soon as it stopped the Doctor turned to look at Piper, his smile fading when he saw blood drip from her nose. He used his sleeve to wipe the blood away.

Stepping out, Harriet pulled Piper in, thanking her for saving them before running off to reassure people that it was over. They made they're way back to the Powell Estate. Rose ran to find her mother while the Doctor went to the Tardis. She felt conflicted. She wasn't sure who she should follow so in the end decided to stay outside and wait for Rose.

Piper looked up to see both Rose and Jackie walking towards her. Jackie was begging her daughter to stay with her. "I'll get a proper job, I'll work weekends and pass my test. If Jim comes round again I'll say no, I really will."

Rose turned to face her mum, smiling softly. "Mum, we're not leaving cos of you. We're travelling, that's all. We'll come back."

"But it's not safe!" Jackie pleaded.

"Mum, trust me. If you saw it out there, you'd never stay home."

"Got enough stuff?" The Doctor asked, looking at the bag she had dumped on him.

"Last time I stepped in there it was in the moment. "Now I'm signing up. You're stuck with us. Ha!" She walked over to Mickey who had been watching quietly. "Come with us. There's loads of room."

"No chance. He's a liability."

Piper's eyes narrowed. She had a feeling the Doctor was lying.

"We'd be dead without him," Rose argued.

"My decision's final."

"Sorry," she turned to Mickey, giving him a kiss goodbye before walking into the Tardis.

In a last attempt, Jackie turned to Piper, knowing if anyone would listen it would be her. "But what if you get lost? What if something happens to him and you don't have any wayof getting back?"

"Jackie, I promise if I need to, I will use my powers to keep herself."

Piper walked into the Tardis, leaving the Doctor outside. She didn't know where she was going but she couldn't wait to find out.