‘Then we have to be clever and not let it come to a fight,’ said the Doctor. ‘We take on the Ice Warriors by outsmarting them.’

‘Are they stupid, then?’

‘No, not at all,’ said the Doctor. ‘They’re really very intelligent. But I’m me.’

‘OK,’ she said, ‘hit me with your clever.’

‘We find out how they’re sabotaging things, and we sabotage their sabotage. That’s how we beat them.’

‘It’s that easy?’ asked Amy.

‘No, that’s going to be ridiculously hard,’ the Doctor said with a sigh.

‘I thought you were super-smart?’

‘Have you seen the scale and size and complexity of this system? It’s going to take me a while to identify exactly what the Ice Warriors are doing, and then I’ve got to work out how to repair or reverse it. And I have to do all of that without mucking up any of the other systems. This is a very finely balanced process. Plus, these terraformers are automated systems. A lot of the component units are sealed because there’s supposed to be no need for manual repair. A lot of them are physically inaccessible. How would you get down there if that needed fixing, for instance?’

She peered over the rail and shuddered.

‘Not to mention,’ said the Doctor, mentioning it, ‘that I’m temporarily without a working sonic screwdriver, which makes everything a gazillion times harder.’

‘It’ll recharge,’ Amy reassured him.

‘I know,’ he said, ‘but we haven’t got a lot of time.

And my biggest concern is not to damage the terraforming systems. My normal approach, as you well know, is to fiddle and improvise, but if I attempt too much of that, I could end up doing more damage than the Ice Warriors. You know what I could really do with?’

‘The Big Book of Terraforming For Beginners?’ she asked.

‘Yes, actually,’ he replied. ‘What I could really do with is the instruction manual that came with this planet cruncher.’

‘It’ll be in the glove box,’ grinned Amy.

Bel came over to them, followed by Samewell. She was wrinkling her nose. ‘What’s that smell?’ she asked.

The Doctor sniffed. ‘Sulphur, from the mantle vents,’ he said.

‘No, there’s something else,’ said Amy.

The Doctor sniffed again. ‘You’re right, Pond,’ he said. ‘I impaired your hearing so your sense of smell has compensated. That’s… decay. That’s something rotten.’

‘Whatever, it’s not very nice,’ said Arabel.

The Doctor was already moving. They followed him along the walkway, through a rock-cut tunnel, and down a metal-lined corridor that opened out into a broad, domed room that looked like some kind of store. By the time they entered it, the smell of putrefaction had become very strong.

‘Ugh,’ said Amy, covering her nose and mouth.

‘That’s rank.’

‘Decaying organic matter,’ the Doctor mused. ‘But why down here?’

The walls of the domed room were lined with rows of plastic-fronted cupboards, each one containing a bio-hazard suit and mask, made for a human.

‘This was a prep area,’ said the Doctor. ‘Scientists or technicians came in here to suit up. See overhead?’ He pointed at banks of blue lights built into the domed roof. ‘UV decontamination lamps,’ he mused. ‘They came in here, suited up and sterilised themselves…’

He went back to the doorway they had entered through. It was a sliding hatch, but it had already been open when they arrived.

‘Look,’ he said. There was a panel of silver metal in the frame to the right-hand side of the hatch.

Something very hot had cut through it, fusing it. The edges of the metal cut looked like melted butter. They were blackened.

‘That’s a palm-scan checker,’ said the Doctor. ‘It operates the lock. Something cut through it from outside to get in here.’

‘Something hot,’ said Amy.

‘I think focused sonics, actually,’ the Doctor replied.

He crossed to the open hatchway on the other side of the domed prep-room. That was open too. Similar damage had been done to the palm-scanner. The smell of rot and decay was much stronger on that side of the room.

‘Let’s see, shall we?’ the Doctor suggested. He went through the open hatchway. They followed him.

On the other side, they found themselves at one end of a gallery space.

The gallery was large and very long. Very, very long. At least a mile long. It was immense. It reminded Amy of an industrial nursery, a massive greenhouse, except that it was underground. Banks of bright, artificial sun lamps ran along the roof, and the galvanised metal floor was lined with rows of deep metal tanks and glass vats. It seemed like something had been growing in here, a considerable crop of things.

The smell in the gallery was awful, like bins left out on a summer’s day, six weeks into a garbage strike.

‘What is this? Are they growing plants?’ asked Amy.

‘Certainly cultivation of some sort,’ the Doctor agreed. ‘I didn’t expect this. Unless…’

He peered into one of the vats.

‘Unless what?’ asked Samewell.

‘These cultivator units have broken down,’ said the Doctor. ‘There’s been a malfunction and they’ve failed.

Perhaps a deliberate malfunction. The reason they smell so bad is that it’s not plant matter they’re nurturing here. These were in-vitro nutrient banks for organic tissue.’

‘Why?’ asked Amy. She climbed up beside the Doctor and peered over into the vat. The stink that wafted up at her was frankly appalling. The vat was basically empty, but from a tide mark on the side, she could see where it had previously been full. The bottom of the tank was filled with a slimy, foul-smelling residue, like something gruesome and decomposing from a horror movie. ‘Oh, that is properly disgusting,’ she announced.

‘Yes, but why?’ the Doctor pondered, tapping a finger to his lips. ‘Why tissue? I suppose this could have been some kind of storage system for organic samples. Maybe the DNA used to build the transrats was kept in suspension in this sort of thing. This may have been a genetic stockpile, a library of animal DNA, so that the Morphans could grow all sorts of strains of creature once the world was ready.’

‘Really?’ asked Amy. ‘So this was… this muck… this was living tissue? Like flesh and blood?’

The Doctor nodded. ‘But the vital support system has failed or been sabotaged. Sabotaged is my guess, from the way the hatches were forced. Now it’s beginning to rot,’ he said. ‘So the genetic database is corrupted.’

He looked at Amy.

‘Or,’ he said, drawing out the word.

‘Or what?’ she asked.

‘Or this wasn’t a genetic library at all,’ he said. ‘It was an organic farm.’

‘How do you mean?’

‘I mean,’ said the Doctor, ‘that someone or something was growing meat in these tanks.’

Amy pulled a revolted face.

‘Like something out of Frankenstein’s lab?’ she asked.

‘Yes,’ said the Doctor, ‘but an awful lot less nice.’

The hatch to the Incrypt waited for a moment, considering the scan of Rory’s palm. Rory stood with his hand pressed to the plate and a sick, fixed grin on his face, frantically working out what he would say when the hatch didn’t open.

He’d just come up with an absolutely killer approach that would absolutely, without question, persuade Bill Groan and the other Morphans he was on the level, despite the non-compliance of the hatch, but then the hatch opened and he never got a chance to use it.

‘You see?’ he said, hoping the billion tons of relief freighting his voice at that moment would not be obvious.

‘Well,‘said Bill Groan.

‘Guide preserve us,’ said Winnowner.

‘We have done you a disservice, Elect Rory,’ said Sol Farrow.

‘ That’s entirely OK and fine,’ said Rory shaking his head and swallowing hard. ‘I understand that you have to be careful, especially with all the… the things that are happening. Shall we?’