The Doctor and Elise followed little Amelia up to her bedroom. In her wall was a four foot long crack shaped a bit like a "W".

The Doctor ran his fingers along the crack as he inspected it. "You've had some cowboys in here. Not actual cowboys, though that can happen", he told Amelia.

"I used to hate apples, so my mum put faces on them", Amelia said, looking down at the apple in her hand.

It had a smiley face cut into it. Elise thought it looked rather weird. Like a small head.

Amelia handed the apple to the Doctor.

"She sounds good, your mum. I'll keep it for later". The Doctor put the apple in his pocket. "This wall is solid and the crack doesn't go all the way through it. So here's a thing. Where's the draft coming from?" He pulled out his screwdriver and scanned it. "Wibbly-wobbly timey-wimey", he said, checking the results, "You know what the crack is?"

"What?" Amelia asked.

"It's a crack. But I'll tell you something funny. If you knocked this wall down, the crack would stay put, because the crack isn't in the wall".

"Where is it then?"

"Everywhere. In everything. It's a split in the skin of the world. Two parts of space and time that should never have touched, pressed together right here in the wall of your bedroom. Sometimes, can you hear...?"

"A voice. Yes".

Growling came from the other side of the wall.

The Doctor grabbed a glass of water off Amelia's nightstand. He chucked the water out before using it to listen to the voice coming from the crack.

Amelia turned to Elise. "Is he always like this?" she asked.

Elise just shrugged.

"Prisoner Zero?" the Doctor asked.

"Prisoner Zero has escaped. That's what I heard. What does it mean?" Amelia asked.

"Prisoner Zero has escaped".

"It means that on the other side of this wall, there's a prison and they've lost a prisoner. And you know what that means?" the Doctor asked.

"What?" Amelia answered.

"You need a better wall". The Doctor moved Amelia's desk away from the wall. "The only way to close the breach is to open it all the way. The forces will invert and it'll snap itself shut. Or..."

"What?"

"You know when grown-ups tell you everything's going to be fine and you think they're probably lying to make you feel better?"

"Yes".

"Everything's going to be fine". The Doctor stuck out his hand and Amelia grabbed it.

Elise held Amelia's other hand as they stared down the wall.

The Doctor aimed his sonic screwdriver at the crack.

It widened, filling the bedroom with a bright light.

"Prisoner Zero has escaped. Prisoner Zero has escaped".

"Hello? Hello?" the Doctor asked.

A gigantic blue eye came out the crack.

"What's that?" Amelia asked.

A bolt of light shot out of the crack and hit the Doctor, who doubled over as the crack closed.

"There, you see? Told you it would close. Good as new", the Doctor said.

"What's that thing? Was that Prisoner Zero?" Amelia asked.

"No. I think that was Prisoner Zero's guard. Whatever it was, it sent me a message". The Doctor pulled out a bill-fold. "Psychic paper. Takes a lovely little message. "Prisoner Zero has escaped". But why tell us? Unless..."

"Unless what?"

"Unless Prisoner Zero escaped through here. But he couldn't have. We'd know". The Doctor ran out into the hallway. "It's difficult. Brand new me. Nothing works yet. But there's something I'm missing. In the corner of my eye", he said, looking around the hallway.

Suddenly, there was a strange bell tolling.

"No, no, no, no, no, no, no, no, no, no!" the Doctor yelled, running down the stairs.

The two girls followed him out into the garden.

"I've got to get back in there. The engines are phasing. It's going to burn!" the Doctor said.

"But it's just a box. How can a box have engines?" Amelia asked.

"It's not a box. It's a time machine".

"What, a real one? You've got a real time machine?"

"Not for much longer if I can't get her stabilized. Five minute hop into the future should do it".

"Can I come?"

"Not safe in here. Not yet. Five minutes".

The Doctor picked up Elise and had her wrap her arms around his neck again before he jumped up on the doorway. "Give me five minutes, I'll be right back".

"People always say that", Amelia told him.

"Am I people? Do I even look like people? Trust me. I'm the Doctor". He jumped back down into the TARDIS.

Elise closed her eyes and clung his neck, nearly choking him.

"Geronimo!" he yelled as they hit the water of the swimming pool again.

The Doctor pulled Elise out of the swimming pool again. Somehow, the Doctor righted the TARDIS and he grabbed Elise's hand. As the Doctor started to run, Elise stood still. "Elise, we do not have time for this!" he said.

Her blue eyes went wide.

The Doctor sighed and knelt down in front of her. "I know you don't understand what's going on, but I promise when this is all over I will explain it to you, okay?"

Elise nodded.

He smiled and kissed her head before pulling out of the smoking TARDIS. He pulled her towards the house.

"Amelia! Amelia, I worked out what it was. I know what I was missing! You've got to get out of there!" The Doctor struggled to sonic the lock on the door. "Amelia? Amelia, are you all right? Are you there?" he asked, running up the stairs, "Prisoner Zero's here. Prisoner Zero is here! Prisoner Zero is here! Do you understand me? Prisoner Zero is..."

Elise watched as a red-haired woman hit the Doctor in the head with a cricket bat.

He dropped to the floor, loudly.

Elise dropped on her knees next to him, shaking him while tiny whimpers left her mouth. She looked up at the redhead and glared at her.

Amy grabbed the small girl and placed her on the stairs, away from the Doctor. "Now you stay right there, young lady".

Elise pouted and crossed her arms over her chest, but did as she was told.

When the Doctor came to, he found a young woman dressed in a police uniform in front of him.

"White male, mid-twenties, breaking and entering. We've also got a potential kidnapping. Send me some back-up. I've got him restrained", she said, "Oi! You, sit still".

The Doctor cleared his throat. "Cricket bat. I'm getting cricket bat".

"You were breaking and entering".

The Doctor tried to get up, but found he was handcuffed to the radiator. "Well, that's much better. Brand new me. Whack on the head, just what I needed".

"Do you want to shut up now? I've got back up on the way".

"Hang on, no, wait. You're a policewoman".

"And you're breaking and entering. You see how this works?"

"But what are you doing here? Where's Amelia? And where's Elise?"

As the Doctor asked that question, Elise came running towards him and dropped into his lap. He smiled at her. "Hello there".

Elise gave him a small smile back.

"Amelia Pond?" the policewoman asked.

"Yeah, Amelia. Little Scottish girl. Where is she? I promised her five minutes but the engines were phasing. I suppose I must have gone a bit far. Has something happened to her?"

"Amelia Pond hasn't lived here in a long time".

"How long?"

"Six months".

"No. No. No. No, I can't be six months late. I said five minutes. I promised".

The policewoman walked away from him and Elise.

"What happened to her? What happened to Amelia Pond?"

"Sarge, it's me again. Hurry it up. This guy knows something about Amelia Pond".

"Are you alright? She didn't hit you or anything did she?" the Doctor asked Elise.

She shook her head.

"Good". The Doctor ruffled her hair and placed a kiss on the crown of her head.

The policewoman came back over to them.

"I need to speak to whoever lives in this house right now", the Doctor told her.

"I live here".

"But you're the police".

"Yes, and this is where I live. Have you got a problem with that?"

"How many rooms?"

"I'm sorry, what?"

"On this floor. How many rooms on this floor? Count them for me now".

"Why?"

"Because it will change your life".

"Five. One, two, three, four, five".

"Six".

The policewoman scoffed. "Six?"

"Look".

"Look where?"

"Exactly where you don't want to look. Where you never want to look. The corner of your eye. Look behind you".

The policewoman turned around. "That's, that is not possible. How's that possible?"

"There's a perception filter all-round the door. Sensed it the last time I was here. Should've seen it".

"But that's a whole room. That's a whole room I've never even noticed".

"The filter stops you noticing. Something came a while ago to hide. It's still hiding, and you need to uncuff me now".

The policewoman started to walk towards the door. "I don't have the key. I lost it".

"How can you have lost it? Stay away from that door! Do not touch that door!"

The policewoman put her hand on the doorknob and opened the door.

"Listen to me, do not open that. Why does no-one ever listen to me? Do I just have a face that nobody listens to...?"

The policewoman was inside the room now.

"Again". The Doctor started searching his pockets for his screwdriver. "My screwdriver, where is it? Elise, have you seen it?"

Elise shook her head.

"Silver thing, blue at the end. Where did it go?"

"There's nothing here!" the policewoman called.

"Whatever's there stopped you seeing the room. What makes you think you could see it? Now please, just get out".

"Silver, blue at the end?"

"My screwdriver, yeah".

"It's here".

"Must have rolled under the door".

"Yeah. Must have. And then it must have jumped up on the table".

"Get out of there. Get out of there! Get out! Get out of there!"

For some reason, the policewoman hadn't come out yet.

"What is it? What are you doing?" the Doctor asked her.

"There's nothing here, but..."

"Corner of your eye".

"What is it?"

"Don't try to see it. If it knows you've seen it, it will kill you. Don't look at it. Do not look".

The policewoman screamed.

"Get out!" the Doctor yelled.

The policewoman came running out of the room and towards the Doctor and Elise.

"Give me that", the Doctor said, grabbing the sonic screwdriver from her. He locked the door and then worked on trying to free himself. "Come on. What's the bad alien done to you?"

"Will that door hold it?"

"Oh, yeah, yeah, of course. It's an inter-dimensional multiform from outer space. They're all terrified of wood".

A bright light emanated from under the door.

"What's that? What's it doing?" the policewoman asked.

"I don't know. Getting dressed? Run. Just go. Your back up's coming. We'll be fine".

"There is no back up".

"I heard you on the radio. You called for back-up".

"I was pretending. It's a pretend radio".

"You're a policewoman".

"I'm a kissogram!" She pulled off her hat and her long red hair came tumbling down.

The door fell to the floor and a workman stood there with his dog.

"But it's just..."

"No, it isn't. Look at the faces", the Doctor told her.

The man started barking instead of the dog.

"What? I'm sorry, but what?" the redhead asked.

"It's all one creature. One creature disguised as two. Clever old multi-form. A bit of a rush job, though. Got the voice a bit muddled, did you? Mind you, where did you get the pattern from? You'd need a psychic link, a live feed. How did you fix that?"

The man opened his mouth, revealing needle like teeth.

Elise screamed and burrowed into the Doctor's side.

"Stay, boy! Her and me, we're safe. Want to know why? She sent for back up", the Doctor said.

"I didn't send for back-up!" the redhead insisted.

"I know. That was a clever lie to save our lives. Okay, yeah, no back up. And that's why we're safe. Alone, we're not a threat to you. If we had back up, you'd have to kill us".

"Attention, Prisoner Zero. The human residence is surrounded. Attention Prisoner Zero. The human residence is surrounded".

Well, that didn't sound good.