She looked back the way she had come. She heard the ruptured hatch shriek open and saw shadows move in the light shining down the vent shaft.

The Ice Warriors were in. They were Ice Warriors, and they had opened the hatch, and they were inside the shaft, and they were coming after her. There was not a single part of that summary that didn’t utterly terrify her.

She had to hurry. She took another step, another, moving faster.

Her foot slipped. She steadied herself again. Then both feet slipped at once, and this time she did not keep her balance.

Amy went over on her backside.

‘Ouch!’ she cried. Then she realised that falling on her bum was not going to be the worst of it.

She was moving. She was sliding. She was travelling down the shaft.

She protested aloud, to no one in particular, and started to paddle and scrabble with her hands and feet.

To no avail. She was picking up speed. She was sliding down the shaft as if it was a chute, on her bottom, like Rory on a monster stupid waterslide. She couldn’t stop herself. She couldn’t get up.

Gaining speed with every passing second, Amy rode the slide, helplessly, deeper and deeper underground.

Snow was falling. It was the blackest kind of night Rory had seen in a long while, cold and enclosing, giving nothing back. Big flakes of snow just seemed to hurtle blindly out of the darkness, zooming at him.

He was following Vesta through the snowy woods.

She had brought her little solamp, but they had agreed to try travelling without it on for as long as they could.

A light could attract the wrong kind of attention. Vesta had assured Rory that she knew which way to go. She knew the woods. She knew how to get them to Beside.

Rory believed she meant it, but he was still worried.

They had left the comforting heat of the autumn mills -

automills, surely? - behind them and set out into a frozen night. There was a very good chance they would die of cold before they got anywhere, and that was without factoring in the it with red eyes that was out to get them.

His clothes had dried out during their stay in the warmth of the mill. He was glad of his coat. He wasn’t convinced it had been worth going back to the TARDIS for it. Maybe the day would have turned out to be rather less energetic if he’d stayed with Amy and the Doctor. Then again, he had no way of telling what sort of adventures they’d been getting up to. He had a fond notion that they would arrive at Vesta’s village, Beside, and find the Doctor and Amy already there, already firm friends with everybody, telling stories, sitting by a hearth, eating hot food. His fond notion had a giant Christmas tree in it too, so he knew some of the details were completely fanciful, but he had hopes.

Rory was also a realist. He tried to count the number of times they had arrived anywhere, by accident or design, and not stumbled into some predicament or other. The only answer he could come up with was zero. It was inevitable, as inevitable as the wheeze of the TARDIS’s console, as inevitable as the Doctor’s sudden grin of insight. These predicaments, Rory believed, naturally attached themselves to Time Lords. In fact, with only one Time Lord left, there was probably a serious backlog of predicaments waiting to be attached. Danger, problems, plight, peril… He wouldn’t be particularly surprised to learn there was some sort of detector circuit aboard the TARDIS that automatically drew them towards trouble. The Doctor would probably admit it one day, casually, as though he thought they already knew. ‘You mean I didn’t tell you about the Predicament Seek-O-Matic Module? I didn’t? I could have sworn… Should I switch it off for a change? Yes, why not? I’ll switch it off.’

Snowflakes continued to stream out of the darkness, become suddenly visible, and hit him in the face. They were like stars. It was like rushing through the cosmos.

It was piercingly cold and blindingly dark, and all he could see were little bright white objects speeding by.

It was like travelling through the universe in the TARDIS and, like the TARDIS, there was no way of knowing exactly where you were going, or how safe it would be when you got there.

Amy was travelling at speeds in excess of anything she was comfortable with, especially given the fact that she wasn’t riding aboard anything like a bike or a skateboard or a luge or a rocket ship, and she wasn’t in any way in control at all.

The lining of the tube felt frictionless, and resisted her frantic attempts to grab hold of something or stop herself. The pitch was also increasing, dropping her down a raked slide even steeper and more alarming than before. Eyes wide, hair flying out behind her, she zoomed down the tube. She realised it was the sort of ride that she might have enjoyed under other circumstances, none of which were presently operating. She also realised she was making desperate, strangled noises like ‘agh’ and ‘eek’ and ‘yrk’.

Then she flew out of the mouth of a tube and landed on a bed of soft, dusty material. She bounced and came to a halt. Coughing, she slowly got to her feet. Her impact had puffed a huge cloud of dusty fibres out of the mass. She was in a small metal chamber, and the dusty material was a thick mass of leaf mould and vegetable fibres that had been sucked into the vent system and had accumulated there to rot. It had probably saved her from serious injury.

Still coughing, she glanced back up the dark tube of the vent system.

‘I am not doing that again,’ she said.

Her feet, striving for some autonomy, chose that moment to skid out from under her and prove her wrong. She slipped, fell down on her rear end again, and shot away down the next extension of the tube system, ‘eek’-ing helplessly.

‘Not fun!’ she yelled at the top of her voice, experiencing an even sharper, steeper, faster ride than before. The tube twisted at one point and almost inverted her, before finally ejecting her into another chamber lined with deep, springy and slightly musty leaf matter.

Amy got to her feet a great deal more carefully than she had after her previous landing. She thought for a moment that she might have damaged her shoulder or back, because it was difficult to straighten up, but then discovered that this had less to do with a sprain or dislocation, and more to do with the fact that she was standing on one of her elasticated mittens.

She let the mitten ping out from under her foot, straightened up properly, and stared into the gloom around her whilst combing bits of dead leaf out of her hair with her fingers.

‘Doctor?’ she called. ‘Doctor?’

The metal chamber, plain and grey and boxy, had several exits, all of which were further tube mouths.

She edged around, making sure not to slip and plunge off on another escapade.

‘Doctor?’

One of the vent tubes ran for a horizontal section, and there was a kind of fluted duct to one side that she clambered through. She was now in a hallway. It was long, metallic and dark. The air was cool but dry. A small amount of ambient light was issuing from recessed lamps in the wall. The lamps looked like smaller and more sophisticated versions of the lights the Morphans used, the devices they called solamps.

The glow reminded Amy of the output of solar garden lights that had been on all night and were beginning to tire.

‘Doctor? Hello?’

There hadn’t been much opportunity to argue with where the tube was taking her, so she wondered how the Doctor, Bel and Samewell could have ended up anywhere else.

Amy listened hard to see if a faraway voice might be answering her calls, and realised she could hear something. It was a humming, a deep resonance. She could feel it more than she could hear it. It was the sound immense machinery made, the steady industrial purr of automation, heard from a distance. It felt as if she was inside a huge factory, the biggest factory ever built, and all the machinery, whirring and chugging away, was hidden from view behind the metal skin of the walls around her.