His companion swung in, wielding the ornate broadsword with both pincers. The first stroke missed.

The red-eyed monster was ridiculously agile and fast.

It somehow slipped under the Ice Warrior’s next stroke, and turned as it rose behind him, burying both sets of front claws in the Martian’s back. Green battle armour shredded. Individual scales twinkled like stars as they showered into the air. Amy flinched as the red-eyed monster lunged its huge jaws forward and ripped into the back of the stricken Ice Warrior’s neck.

The other Warrior had regained its footing. As the red-eyed thing savaged his comrade’s throat, he swung the axe. It struck the monster squarely in the right shoulder. Ugly, unhealthy-looking blood sprayed from the wound. The monumental impact smashed the redeyed thing off its prey and clean through the guard rail.

It fell.

It did not fall far.

With extraordinary gymnastic skill, it snagged the struts on the underside of the walkway, and swung under the bridge, somersaulting up, free, on the other side. It landed on the Ice Warrior with the axe from behind, knocking him over, face-first, into the half-broken guard rail. Entangled, they fought brutally with each other, each one trying to break the other’s grip.

The red-eyed monster tore away first, but only so it could pull back and put all its inhuman strength into a driving hook that ripped across the Ice Warrior’s face, shredding his visor.

The Ice Warrior, mortally hurt, staggered backwards, hissing like a punctured tyre, and toppled over the torn rail. He dropped away into the flaming abyss below.

The other Ice Warrior, bleeding from his jagged wounds and ruptured scale-armour, came at the redeyed thing, swinging his sword. The thing evaded the first two strokes, and then drove at the Ice Warrior, catching the side of the razor-sharp blade with its cybernetic hand. It plucked the sword out of the Ice Warrior’s grip and threw it away. Then it went for the Ice Warrior’s throat. The Ice Warrior clawed at it, grabbing it by the neck and shoulder with his powerful clamps. Locked together, they wrestled ferociously for a few seconds.

The Ice Warrior, understanding that he was weakening and bleeding out, understanding that he was up against an adversary who was stronger, faster and essentially superior, understanding that he was effectively beaten, did what all dedicated warriors do as a last resort. Gripping the red-eyed thing that was busy killing him, so tightly that it couldn’t break free, he lurched off the walkway too. He took his redeyed tormentor to its doom alongside him.

They vanished from view in the fires far below.

Amy, trembling, looked at the two young Morphans.

‘Let’s get out of here,’ she said. ‘You know, before something else really, stupid well insane happens.’

But it was too late. There were more of them, more of the red-eyed things.

They were stalking out of the hatch and onto the bridge, advancing towards the three, defenceless humans.

Rory, Vesta, Winnowner and Jack Duggat backed into the assembly hall, trying not to make any hasty movements. Jack still had hold of his hoe, but not in any way that suggested he was likely to wield it.

The red-eyed It that Vesta had seen in the woods prowled in after them. Gazing at them, it padded through the snow like a leopard on all fours, frost glinting on its matted mane of tubes and wires. It smiled an eternal, unintentional steel smile.

It entered the wood-panelled hall, and looked around, as though sensing something familiar. It returned its crimson gaze to the four terrified humans and stared at them. Then it rose on its hind legs and stood upright like a man, an adjustment that was somehow even more distressing.

‘Oh, save us,’ whispered Winnowner. ‘What has Guide wrought?’

‘Guide,’ the thing echoed. It was a horrid, sticky sound, a rumble that was part growl and part phlegm.

Its fearsome teeth made normal speech impossible, but it gurgled the word out of a small, cybernetic vocal implant that they could see in its throat, now that it was standing upright.

It was so frighteningly tall.

‘Guide…’ it repeated. ‘I… am assigned to secure and protect… the Guide system.’

‘The Guide?’ asked Winnowner.

‘The Guide system… must not fall… into enemy hands. Aggressors have been detected… tampering has been detected… purge now under way.’

It raised one gnarled, part-metal fist and wiped droplets of blood off its awful teeth.

‘I… am assigned to secure and protect… the Guide system. It is… here.’

‘What are you?’ asked Rory.

‘Transhuman sixty-eight of one hundred fifty…

woken and refitted for this Category A emergency…’

‘Woken?’ asked Rory.

‘From… the cryo-store,’ it replied. ‘Stand aside… I am assigned… to secure and protect… the Guide system.’

They wavered.

‘I am… sanctioned to slay… anything that stands in opposition to my task…’ it said.

They got out of its way. It dropped back onto all fours and padded past them.

‘I never asked for this!’ Winnowner said. ‘I just asked for help! I never expected that any of the patients would be woken!’

Rory looked at her sharply. ‘Wait, you said “woken”

too! What do you know?’

‘Only what I must know!’ Winnowner snapped. ‘The secret that passes from one generation to the next, through the last in each line. The secret that I must pass to Elect Groan before the end of my time.’

‘I think you should share it with the room,’ said Rory, ‘because your time could be up any second now.’

‘No!’ Winnowner said.

‘What is this?’ asked Vesta. ‘Winnowner Cropper, what is this?’

‘Winnowner?’ Jack urged.

‘I will keep Guide’s secret. It is not my place to tell.’

Winnowner’s voice dropped low. ‘I will keep it to the end, for the good of all Morphans.’

‘I don’t think that’s anything like good enough right now,’ said Rory.

‘Tell us what this thing is and what it wants!’ Vesta demanded.

‘Be silent!’ the red-eyed thing growled, turning back to them and rising up again. ‘Or I will… silence you.’

‘I don’t think that would be very friendly at all,’ said the Doctor. ‘Especially not as you’re all supposed to be on the same side.’

Light levels in the assembly had shifted. The shimmering effect of the holographic telepresence field was rising like mist from the metal circle patterns inlaid in the old wooden floor. The Doctor was in their midst, sitting in a high-backed chair, facing a white control console. He got up and walked over to face the beast.

‘Sorry I couldn’t get here earlier. I was trying to tune in,’ he said. ‘Very difficult, when you haven’t got a reliable Guide.’ He glanced at Rory. ‘Everything OK, Rory?’ he asked.

‘Oh, you know, Doctor,’ Rory shrugged. ‘Apart from the Ice Warriors, and the spaceship shooting the place up, and that thing there, everything’s dandy.’

The Doctor nodded and looked back at ‘that thing there’. It growled softly.

‘A Transhuman construct,’ he said. ‘Advanced martial model. Part of an emergency protocol. A last resort. If the terraformers are threatened. The plantnations don’t have any actual weapons. They don’t have guns or anything. This is what the system manufactures if a weapon’s really needed.’

‘If the Morphans are threatened,’ said Winnowner.

The Doctor shook his head. ‘Sorry, no, actually.

They don’t really care about you. You’re just… the help.

In the long run, you’re expendable.’

‘Winnowner said she had a secret,’ said Rory.

‘I’m sure she does. Last of her generation. The dark and murky legacy. The sort of secret that would make life unbearable for the Morphans if they knew about it.

The sort of secret that makes you oh-so protective of your Guide Emanual. You had to pass the secret on eventually. Who were you going to tell, Winnowner?