Ace threw the Nitro-9 into the middle ground between them; perhaps the explosion would catch the horse creatures off-guard. They could escape under cover of the smoke, at least be harder to hit …

As the Astingir leader bellowed, ‘Fire!’ the Nitro-9 ignited. It was a good blast, and Ace’s heart danced like the flames that erupted from inside, smiling as the black smoke came roiling out. She turned to the Doctor and grabbed his arm. ‘Come on, then …!’

But he shushed her as tremors came shaking through the ground. Awful, whinnying screams came from the Astingir, fading as the vibrations increased.

‘What’s happening?’ Ace shouted over the thrum and rumble.

The Doctor had already turned to run again, making for a dark mouth in the wall nearby. They passed through it and up a rubble-strewn slope. Reaching the crest, Ace could see the TARDIS nestling blue and solid in the broken, half-baked landscape.

As she looked back, she saw what she’d done. The Nitro-9 had blown an enormous chasm in the desiccated floor, and the foundations had collapsed beneath. The blackness left behind was that of an abyss. All trace of the horse creatures had vanished save for a single golden bow lying at the edge of the split.

‘The Astingir,’ Ace whispered.

The Doctor was mopping his face with his paisley cravat. ‘The floor gave way under them.’

‘Then … they’re dead?’

‘You couldn’t have known,’ the Doctor told her quietly. ‘And they would have killed us. You had to do it.’

‘I always have to, don’t I?’ Ace said. ‘It’s why you keep me around.’

They made their way up the blasted hillside in silence, until the crumbling city lay far behind them and they reached the cool, bright safety of the TARDIS. Ace leaned against the console and felt herself trembling, and not only from her exertions. It was one thing to blow a Cyber patrol to smithereens, or to beat the hell out of a Dalek. But the Astingir were living beings, strong and wild and fast, and only there at all because the Doctor had forced them to be, manipulating them just like he manipulated everyone. Manipulating her.

And I killed them. All of them.

She watched him brush the dust and detritus from his hands and clothes, unaware of the dirt piling on the floor about him. She felt so tired. And they burned in her mind again, the visions hammered hard from the Anvil. The snatches of so many other lives away from here … the fragments of futures she could embrace or avoid. Build or destroy.

Or fight for.

The Doctor rolled his hat up his arm so that it landed neatly on his head. ‘Well, Ace! Where to next?’

‘Professor …’ Ace looked down at the floor, and swallowed hard. ‘Professor, this is the day we say goodbye.’

Part Three

2020 AND BEYOND …

CHAPTER EIGHTEEN