When River and Aderyn appeared on the rooftop they were both smiling.

"Amy, Doctor," River said happily "And the plastic Roman."

"Don't worry, he's on our side. Let me explain," Aderyn paused then shook her head "No there is too much, let me sum up. This is Rory, he's Amy's fiancee. He died, got erased from time then came back as a Roman."

"Ok, makes sense," River said. "I have questions. But number one is this, what in the name of sanity," River turned to face the Doctor "Have you got on your head?"

The Doctor straightened his bow tie and tipped the fez so it was at a jaunty angle "It's a fez. I wear a fez now, fezzes are cool." Amy leapt forward, seizing the fez from the Doctor's head. She threw it high into the air. River aimed, keeping the offending hat in sight, and shot it. The fez vanished in a swirl of red tatters.

"Try a beanie hat next time." Aderyn said to him. The comic relief the destruction of the fez had provided soon vanished when they heard the robotic cry of "exterminate!" and the Dalek raised into view over the parapet.

River pushed Aderyn and Amy towards the open hatch. The Doctor raised the satellite dish, using it as a shield as they scrambled back through the hatch.

Keeping her weapon unholstered, River turned this way and that, guarding the group at the bottom of the ladder. The Doctor stayed at the top of the ladder, listening intently.

"Doctor, come on." Aderyn hissed.

He held up his hand to shush her. She crossed her arms and tapped her foot impatiently.

"It's moving away, finding another way in. It needs to restore its power before it can attack again. Now, that means we've got exactly four and a half minutes before it's at lethal capacity." he said eventually, dropping easily down the ladder.

"How do you know that?" Rory asked.

The Doctor stopped walking and turned "because that's when it's due to kill me."

"Kill you?" River exclaimed "What do you mean kill you?"

"Oh, shut up," The Doctor replied moodily "Never mind that. How can that Dalek even exist? It was erased from time and then it came back."

"The light from the Pandorica, that's what you said." Amy said.

"It's not actually a light, it's a restoration field," the Doctor called as he ran down the stairs, his voice echoing throughout the museum. "That light brought you back, Amy, restored you, but how could it bring back a Dalek when the Daleks have never existed? When the TARDIS blew up, it caused a total event collapse. A time explosion. And that explosion blasted every atom in every moment of the universe."

Aderyn stopped walking "Can we not run and talk at the same time, this is doing my head in?" The Doctor stopped walking, he turned to face her. He looked as though he were about to say something, but shook his head. "So the explosion destroyed every atom except what was inside the Pandorica. The perfect prison. And inside it, perfectly preserved, a few billion atoms of the universe as it was. In theory, you could extrapolate the whole universe from a single one of them, like cloning a body from a single cell. And we've got the bumper family pack."

Rory opened his mouth, closed it again then shook his head "No, too fast. I'm not getting it."

"That's insane. Doctor, you're being completely ridiculous. The Pandorica partially restored one Dalek. If it can't even reboot a single life form properly, how's it reboot the whole of reality?" Aderyn snapped.

The Doctor rolled his eyes at her "Oh trust you to find a flaw." he said.

"A flaw in what? I'm with Rory on this one. I'm not getting it." Amy said.

"The box contains a memory of the universe, and the light transmits the memory, and that's how we're going to do it. Relight the fire. Reboot the universe,"The Doctor said triumphantly "But what if we give it a moment of infinite power? What if we can transmit the light from the Pandorica to every particle of space and time simultaneously?"

Aderyn frowned at him "Well, that would be lovely, dear, but we can't, because it's completely impossible." she said putting angry emphasis on the last two words.

"I have a plan." he said. He began to walk down the stairs again. Aderyn caught up with him on an upper corridor. She grabbed his arm and spun him round. "I'm fed up with running up and down these stairs," She said "So before you go any further can you please tell me what the plan is? And why it involves running up and down the stairs so much?"

The Doctor looked at her. He stayed silent for a moment before speaking slowly and calmly "My life is about running, you should know that," He smiled at her and was relieved when she smiled back.

"Now come on, lets kick start the second big bang." He was just about to go down the next flight of stairs, when out of nowhere, an energy beam hit the Doctor. He fell to the floor, his clothes smoking. Rory, Amy and River ran down the remaining stairs. Amy pulled Aderyn away from the open door she had been next to.

"Doctor!" Aderyn shouted. She made to run towards him, but Rory held her back. He looked through the door and saw the Dalek. Stepping in front of her, he shot the Dalek. It powered down, apparently dead. He let Aderyn go, but she didn't move. She watched as the Doctor activated the manipulator.

"Where did he go?" River said.

"Downstairs, twelve minutes ago." Aderyn said quietly.

"Lets got then." River said, she turned to run down the stairs.

"River, he died." Amy said. The Dalek whirred back into life "Systems restoring," It said "You will be exterminated."

"Go," Aderyn said "go to the Doctor."

"Aderyn we are not leaving you here. Come on." Amy said, she tugged on Aderyn's sleeve. But Aderyn didn't move. Instead she drew her weapon, her stare fixed on the Dalek.

"You will be exterminated." It said again.

"Oh no, I really don't think so," Aderyn said, her voice dangerously calm "Your systems are still restoring, which means your shield density is compromised. One Alpha Mezon burst through your eyestalk would kill you stone dead." she raised her gun.

"Records show you will show mercy. You are an associate of the Doctor's." The Dalek inched closer to her.

"I'm the little bird with the broken wing. I think you should check your records again." She said. The Dalek paused, then backed away.

"Mercy!" it cried.

"Say it again." Aderyn whispered.

"Mercy!"

"One more time." Aderyn flicked a switch on the side of the gun, charging it instantly to maximum power.

"Mercy." The Dalek backed itself against a wall. Aderyn fired, her shot hitting the Dalek's eyestalk. She glared at it before turning away.

"You're not the only gun toting psychopath round here." She said to River. Aderyn left them stunned as she started to walk down the stairs.

"Aderyn," River said, running after her "That Dalek was scared of you."

"I know." Aderyn said.

"Why?"

Aderyn stopped walking, waiting for them to catch up. She turned to face River as she drew level "I've encountered them before, with the Doctor. Let's just say they didn't like me very much."

When they got down the stairs, they found the Doctor had gone.

"Where did he go?" Amy said, rushing ahead of Aderyn, who kept walking, turning towards the Pandorica exhibit.

"The Doctor said he died. But the Doctor lies." She said bitterly.