‘A rat factory?’ asked Amy. ‘Making easy-to-build rats?’

‘Flat-pack rats,’ the Doctor agreed. He swung the rat he was holding around by the tail like it was a bolas.

‘Easy to build. Disposable.’

‘But why?’ asked Amy.

‘Presumably because there’s something wrong,’ said the Doctor. He stopped spinning the rat, realising it was pretty undignified for both of them.

‘The terraformer system has detected a loss of efficiency or some other defect,’ he said, ‘and it’s automatically starting diagnostic procedures to address it. Transrats would be a first step. Build some, release them into the systems, clean out any dirt, or clutter, or infestation, or glitches.’

‘Glitches, huh?’ said Amy. She looked at the ratthing the Doctor was holding. ‘They seemed really hungry.’

‘Because they’re not the solution to the problem afflicting the terraformers,’ said the Doctor. ‘It’s not a problem you can eat.’

‘But if they got out,’ said Bel. ‘They’d attack sheep…

goats…’

‘They might,’ the Doctor agreed. ‘Hungry, and outside the system control of the terraformer, they could go on a frenzy. That would explain the livestock kills.’

‘So the Ice Men haven’t been killing and devouring sheep, then?’ asked Amy. ‘ Warriors. I meant Warriors.’

‘No,’ said the Doctor, ‘which sorts out one of my original problems. I suspected Ice Warriors from the start. The moment I realised that something was trying to manipulate an entire planet’s climate and make it colder, I immediately thought of Ice Warriors.’

‘Well, who wouldn’t?’ asked Amy.

‘Quite,’ said the Doctor.

‘That was your hunch? The hunch you said you’d got?’

‘Yes,’ replied the Doctor. ‘It fitted the modus operandi of the Ice Warriors, except for one small detail. They’re herbivorous.’

‘So they wouldn’t be eating livestock,’ said Amy, ‘but these rats would.’

The Doctor swung the dead rat by the tail like a conker on a string. ‘Yes, if they got out. But the terraforming system should be sealed enough to prevent them escaping into the wild.’

‘You reckon the Ice Warriors broke into the terrafirmer and did something to sabotage it,’ said Amy, ‘and you also reckon the terrafirmer detected that sabotage as a problem and built the transrats to deal with it. Makes sense that the transrats would have got out through whatever hole the Ice Warriors made to get in. That’s how they got out and started eating sheep.’

‘Nice deduction, Pond,’ said the Doctor.

‘Why would these Ice Warrior things attack the Firmers, though?’ asked Arabel.

‘Because they want an Earth-like planet too, but their idea of Earth-like is colder not warmer,’ replied the Doctor.

Arabel shook her head. ‘I don’t…’ she began.

‘Your ancestors,’ said the Doctor, ‘the original Morphans, were looking for a planet like Earth.’

‘Like Earth before?’ asked Samewell.

‘Yes, like Earth before. But the chances of them finding a world that was exactly like Earth before were slim. I mean, the variables are huge. The best chance they had was to find a planet that was sufficiently like Earth—’

‘Earth-esque,’ said Amy.

‘Precisely right,’ said the Doctor. ‘If they could find a planet that was sufficiently Earth-esque, then they could use the sophisticated terramorphing systems they had on their colony ark ship to tweak the climate and make it perfect. That’s what you’ve been doing for twenty-seven generations. You’ve been watching over things while the terrafirmers tweak and finetune Hereafter to make it just right.’

‘And these charming Ice Warrior blokes,’ said Amy,

‘have a very different concept of just right.’

‘They need an Earth-like planet too,’ said the Doctor,

‘but their idea of Earth-like is not like your idea of Earth-like, it’s like—’

‘Way too many likes there, Doctor,’ said Amy.

‘OK, in broad terms you’re both looking for the same sort of world, but their ideal environmental baseline is between fifty and seventy-five degrees cooler than humanity’s.’

‘So they’re fighting against us?’ asked Arabel.

‘I’ve known them sabotage biomes before,’ said the Doctor grimly. ‘I’ve seen them doing their own terraforming. I even saw them try it on Earth once. On Earth before, before Earth before was lost. I’ve never seen them hijack someone else’s terraforming system and recalibrate it. Typical Ice Warrior pragmatism.’

‘How did you stop the rats?’ Samewell asked. He copied the Doctor and picked up one of the dead rats by the tail.

The Doctor put down the rat he was dangling. He fished his sonic screwdriver out of his jacket pocket. ‘I noticed the enhanced acoustic sensors,’ he said. ‘I guessed they’d be particularly sensitive to sonic attack.

I hoped a little high-frequency burst would be enough to zap them or drive them off.’

‘And deafen me,’ said Amy.

‘I trusted your ears wouldn’t be quite as sensitive as theirs,’ said the Doctor.

‘Well, I’ll take earache over being eaten alive by rats any day,’ Amy started to say.

Samewell let out a screech of alarm. The transrat he’d picked up wasn’t dead. It suddenly shivered, twitched, and woke from the fugue state the Doctor had blasted it into. Its huge jaws opened like a spring trap. Massive steel-veneered teeth gleamed in the half-light. Swinging itself by its tail, the rat started to snap and gnash at Samewell.

‘Put it down!’ Bel yelled.

‘Don’t put it down! Keep it at arm’s length!’ Amy shouted.

‘Aaaaaaaaaahhhh!’ Samewell observed.

The Doctor clicked open his screwdriver and calmly aimed it at the aggressive creature. Nothing happened.

‘Ooops,’ he said.

‘Doctor!’

He fiddled with the screwdriver.

‘I’ve asked too much of it today already,’ he said,

‘what with noise-cancelling the Ice Warriors and zapping the transrats, it’s really drained. It’s gone into sleep mode.’

‘Doctor!’

Amy lunged and grabbed the rat’s tail out of Samewell’s grip. He was still yelping in alarm. The transrat snapped at her repeatedly, trying to chomp her arm or her face.

‘Yeah, yeah,’ Amy snarled and swung it by the tail hard into the tunnel wall. It went limp and she dropped it. ‘Worked last time,’ she said.

‘Who is this Rory?’ asked Bill Groan.

‘He’s my friend, Elect,’ replied Vesta. ‘We met in the woods. We were both threatened. He looked out for me.’

‘I see,’ said Bill Groan.

‘I may have hit him on the head with a mallet too,’

Vesta admitted.

‘But that’s totally not important,’ said Rory.

‘He’s a stranger,’ said Chaunce Plowrite.

‘Yes,’ said Vesta.

‘Another stranger,’ said Old Winnowner. ‘That’s three today.’

A hush had fallen on the assembly. Everyone was staring at Vesta and Rory. Rory felt pretty uncomfortable. In the solamp light, the faces around him were stern and unforgiving. They seemed to be searching for answers, as though they might peel back or melt away his skin to find the secrets they were looking for. There was pent-up emotion in the hall.

These were people who had lived hard lives and, no matter how hard they worked, they did not expect those lives to change. Something profound mattered to them, something that threatened what little comfort and solace they had in their lives, and they wanted answers.

Despite sensing that, Rory could not help asking the question.

These other strangers, the other two? Were they… a girl with long red hair and a tall bloke?’

Everyone around him started muttering and chattering.

‘He admits to knowing them,’ said Old Winnowner.

‘Are they here?’ asked Rory.

‘They were here,’ said Bill Groan. ‘They escaped.’

‘How could they escape?’ asked Rory. ‘What did they escape from? Why did they need to escape?’