‘They’ll just clear the path and ride on through,’ Ace puffed.

‘Keep going,’ the Doctor told her. ‘They’ll run out of arrows in the end.’

Ace did keep going, of course she did, it wasn’t in her nature to stop. But as she and the Doctor kept up their sweat-soaked sprint through the burnished ruins, she glimpsed movement to the side, and then movement up ahead, and heard galloping hoof beats like the soundtrack of her heart. This had been the Astingir’s world once; they knew the landscape and were fanning out, overtaking and outflanking the fugitives. Wearing them out. Driving them toward territory better suited for the showdown.

‘They’re playing with us,’ Ace realised.

The Doctor gave her a mournful look. ‘I don’t suppose they get much chance for a chase here.’

Ace kept going, looking all about for somewhere to hide. There were deep fissures in the ground here and there, but the sides were smooth, with no ledges to climb down out of the creatures’ reach. There were buildings with doors wide open, offering shade and shadows for hiding places, but the horse creatures could simply play them at their own game, loose off a couple of arrows and crush them in moments.

The Doctor led the way up a steep, smooth slope, leaning on his umbrella for balance, poking handholds for Ace with the metal point to help her climb. They heaved themselves onto a ruin of stained-black concrete, wide, crumbling walls but no roof. The cracked stumps of pillars rising around them like fingers on a closing fist. Again, Ace shuddered at the touch of the Wraiths inside her. Her head felt itchy, sweat was pouring down her face.

With a groan, a wall toppled and fell inward to reveal all eight Astingir cantering through the thick clouds of dust like sinister spectres, dark eyes fixed on their prey, bows and arrows raised.

Ace looked at the Doctor. ‘Back the way we came?’

‘Away from the TARDIS? No use.’ The Doctor shook his head. ‘You wouldn’t be carrying …?’

‘Nitro-9.’ She nodded, fumbling in her backpack for a canister.

‘Remain still.’ One of the horse creatures was leading the others slowly forward. ‘You are trespassing on our world. You have defiled a Site of Mass Contrition.’

The Doctor raised his hat again. ‘For which I imagine you’ll want to take us prisoner and place us on trial?’

‘The punishment, under Article 26 of the Pan-Conflict Termination Treaty, is immediate execution.’ The leading Astingir turned to his squad. ‘Firing party …’

‘Wait!’ Ace shouted. ‘We didn’t know …’

Didn’t know … Again, the voices of the Wraiths, echoing through her own thoughts. She screwed her eyes tight shut and cracked open the can. It hissed angrily, the timer fuse counting down.

‘Take aim.’ The Astingir carefully aimed their bows, the air shimmering about them with the heat of the coming blasts.