"A volcano in London?" Jack sounded more than a little sceptical.

"Apparently," the Doctor said, "although...it doesn't have to be a volcano. Lots of reasons for nature going haywire. Could be anything." He looked around, as if for inspiration.

"Then why are we here?" Jack asked him. "Why aren't we where it happened? When it happened? What's the point in bringing us here to see the carnage. I'm telling you, Doctor, they're toying with us."

The Doctor didn't reply and by some unspoken agreement, they walked along the thin ledge of pavement that separated them from the swirling waters. Donna found it was easier to pretend that the entire place was unknown to her. Better to look at the water, then the houses above it that she had spent her childhood running alongside. Better even to focus on the the sky which was a colour it should never be and the straggling plants in the cracked earth that wouldn't have survived on British soils for more than a few minutes in her time. Better to pretend it was a whole new planet, a different world altogether.

Now they were drawing near to the group of people who were watching their approach with apprehension on their faces.

"Hello," the Doctor said cautiously, "could you tell us..."

He got no further. The four people leapt to their feet, never taking their eyes off the Doctor.

The Doctor stared calmly back and quietly, he spoke again.

"It's ok. We're here to help. I'm the Doctor, this is Donna and those two behind me..." Lowering his voice, he whispered to Donna, "neither of them are brandishing guns, are they?"

Donna shook her head.

"...are Jack and Jenny," the Doctor finished. "And you are...?"

But the people still stared at him in undisguised horror. One of the girls tugged at the sleeve of the oldest man and gestured towards his coat.

"They're armed," Jack murmured and as his hand went to his coat, he stepped smartly in front of the Doctor. As one, the group of people stepped rapidly backwards.

"Don't you dare, Jack" the Doctor muttered, never taking his eyes off the group huddled in front of them, "particularly on my account."

Jack inclined his head slightly to murmur back:

"Always on your account, Doctor. I told you before, I like this regeneration."

The Doctor opened his mouth to respond but in the same instant, one of the men pulled a ragged linen bag out of his coat and threw it at the Doctor's feet. He turned and ran, his companions in close pursuit.

"It's like they couldn't understand us," Donna said.

"Quite possibly," the Doctor said, his face troubled.

"Is the world really this far gone?" Jack asked.

"Apparently." The Doctor bent down and picked up the bag that the man had dropped. He opened it cautiously and held it out to Donna.

"This is what they thought we were after," he said.

The bag contained three tins of food, the labels torn and tattered.

"And this is obviously valuable," Jack said flatly.

"We should go back," Jenny said, her voice urgent.

"I agree," Jack said, "we can't do anything from here. All we can do is go back and make sure this never happens. We know it's not supposed to be in our future."

"We keep going," the Doctor said, "we can't change anything without knowing what exactly we're changing."

"It's not safe," Jack replied and for some reason he glanced at Donna as he said it, "there's floodwater everywhere. We don't know the patterns. You can't predict what they're going to do!"

For a long moment, they faced each other and Donna could almost sense an invisible battle of wills. She bit back the angry question she'd been about to ask about why they were both suddenly treating her as if she were a china doll.

"We need answers," the Doctor said quietly.

"Fine." Jack turned away and marched ahead of them.

Donna wondered if she was imagining it but the Doctor looked quite smug.

"Men," she muttered to Jenny who looked up at her as if startled at the sound of her voice. Donna looked closely at her.

"You look terrible. Are you ok?"

Jenny nodded but she was so pale that her face almost looked transparent. As she walked alongside Donna, something in her movement suggested that every step was an effort.

"What's wrong?" Donna asked, holding out an arm to stop her.

"I'm fine," Jenny said. Her voice sounded strange and flat, more like an echo of itself.

Donna kept hold of her arm and looked ahead, opening her mouth to call the Doctor but she stopped when she noticed where she was. The local park. Her favourite spot for a morning coffee on the way to work, or a stroll by the river at weekends.

Now it was a forest.

Somewhere in the distance, the sound that should have been the slight drip and ripple of the river was a rushing, pulling sound like a stormy ocean. Around them, plants and shrubs curled around the trees, completely covering the stones and benches she knew so well. A stream wound its way down a slope ahead of them. Everything was green and wild and full of movement, a furious spiralling all around them.

"It's...." She stopped, unable to say anything more. The bag of food dropped from her hand and the tins rolled through curled pathways between roots and ragged weeds. She barely noticed.

From somewhere in the distance, the sound of the wind and water sounded like laughter, as if nature itself was amused at their efforts to keep abreast of it.

"Sounds like children playing," she said, hoping her voice didn't give away the sudden rush of fear that ran through her.

Jenny raised her head, listening.

"It wasn't us," she said suddenly.

"What?"

"It wasn't us," Jenny repeated. "This didn't happen because of anything we did. That's why we can't stop it." Her voice still had the sound of someone dreaming.

"'Course it wasn't us," Donna said. "Is that what you're worried about? It's not your fault, Jenny. The Doctor knows that."

"You don't understand."

"Donna!" The Doctor's voice drifted back to her, "Keep up!"

"We're here...we're coming!" She shouted back. She took hold of Jenny's arm once again and they made their way slowly forward until a sound behind her make her turn back.

"That sounds like..."

A soft whirring sound so familiar that even when it came as a shock, it was a nice one.

"The TARDIS?" She saw Jack turn to the Doctor in bewilderment. "Did you...?"

The Doctor shook his head.

Donna watched as the familiar blue shape began to come into view. For a mad moment, she wanted to laugh at the thought of its wobbly landing on the uneven ground of the forest.

The forest.

The tin of beans.

She called frantically to them.

"It's us, Doctor! It's me and Jenny! This is where we came to that night!"

The Doctor ran towards them, beckoning furiously.

"Out of sight! Now!"

"Come on!" Donna tugged Jenny's arm and shouted at her when the girl didn't move.

"Jenny! Come on! We didn't see anyone that night so we're not supposed to see anyone now! We've got to hide!"

How weird to think she'd been here that evening watching herself.

Jenny wrenched her arm free, glanced briefly at Donna and began to run away from her, her gait unsteady.

"Jenny!" Donna screamed at her. "You can't! You didn't see anyone that night! You didn't see..."

She trailed off.

"Did you see yourself?"

The TARDIS door was opening.

Jenny continued to run down the slope and towards the sound of water. Giving her one last, hopeless look, Donna ducked into the nearest line of trees and followed her. She didn't dare look behind her. Seeing herself here seemed so completely wrong she couldn't bear the thought of it.

Keeping Jenny in her line of sight, she made her way downwards until she found the Doctor and Jack.

"She's going to see herself," she said to the Doctor and her voice was trembling so badly, she could hardly say it.

"I know," the Doctor said shortly. His eyes were fixed on Jenny as she made her way to the edge of the water. She felt Jack's hand on her shoulder.

Jenny bent over when she finally stopped, as if trying to catch her breath.

"The other Jenny will be here in a second," Donna said.

"We can't interfere with that," the Doctor replied.

"She's not well."

"I know."

"When why aren't you doing something about it? Why won't you help her?"

"I'm trying to," was all he said.

But even as they watched, Jenny looked to be trying to keep herself upright. There was something about her, something desperate and lonely, something looking for help...

"Sorry." Donna hardly realised what she was saying before she said it, "I can't watch this."

Just as Jenny had done to her, she wrenched herself from Jack's grip and ran.

"Donna, no!"

But she kept going, aware of the few seconds she had before the other Jenny would arrive.

Jenny was watching her approach as if she had known that she was coming.

"We have to leave here," she whispered.

"The Doctor thinks it's more important we stay," Donna told her, "it's alright. We'll..."

But as she spoke, Jenny sagged sideways and fell on to the sodden ground.

"Jenny!"

She bent and cradled the girl in her arms. Jenny's eyes were half-closed and her skin was deadly cold.

In the same moment, there was a flurry of running footsteps and Jenny, the other Jenny reached the river. Like her prone counterpart, she stopped for a second, taking a deep breath before looking around her. Donna watched as she realised what and who she was looking at. She stopped dead.

"Donna?" she whispered and the word came out as a gasp.

For a second, nothing moved. Even the water and the movement of the trees seemed silent, as if the whole world was holding its breath.

A voice, her voice sounded over the quietness. Jenny's face, frozen at the sight in front of her, turned in its direction and with a final, helpless glance at them, she turned and made her way back up the slope and back towards the stream where another Donna was rushing towards her, to guide her safely home.