Now her senses were being overwhelmed by the smell of nitric acid and the past exploded into her head. It was as if she was back in her bedroom again, perfecting her homemade explosive in the improvised laboratory she had set up.

‘Are you stinking the house out again with those horrible chemicals of yours?’

Her eyes began to stream, but Dorothy couldn’t tell if it was because of the nitric acid or because of the sheer strength of the moment. With a cry of despair she ran forward, fists clenched, all the resentment of childhood that she had thought had been successfully buried surging to the surface once more.

‘Who are you?’ she yelled. ‘Why are you doing this?’

Then something the Doctor had said in the batcave came back to her: ‘Time Dilation Syndrome.’ Graham might have switched off the cloaking shields in the present but the effect had tumbled through to the past.

What was being switched on now that was bringing her own personal past back to haunt her?

The Doctor strode down the station’s sinewy corridors, sonic in one hand and white flag – a slightly used hanky tied to an old car aerial – in the other. Everything depended, she knew, on how deeply the Astingir had scanned the station. If they already knew who she was, no words would make a difference.

She was dead.

Before long she reached the cavernous space that formed the Functional Abyss – the charged space at the station’s core. The Doctor felt the hairs on the back of her neck stand up at the potential of the place: soon, enough subatomic particles would be crunched to bore a quantum portal through local space-time. Whatever was collected from the Earth below would arrive here and the transmat signal, boosted a quintillion-fold, would shoot it across the stars to wherever it was expected.

If the Astingir had come here, the Doctor reasoned, then perhaps they knew the destination of the transmat and were following the trail backwards. If they could be persuaded to part with that info, it could save a lot of faffing about. They could pool their resources, find whoever was responsible for the abductions from Earth and rescue those who’d been taken. The Astingir would make good allies.

Unless, again, they knew who she was.

The Doctor thought of Ace and sighed. I should never have let you go, that day, she thought. She closed her eyes.

A sudden thick stench of burning flesh caught in her nostrils, stinging her from her reverie. A huge chunk of burnt-toffee bone fell smoking from the wall beside her. On the other side she glimpsed two golden hooves glowing white with energy; a clatter, and a dark, equine head pushed through the smoke. The eyes were dark and gleaming, the mane plaited with thin strips of white metal, which denoted rank as well as giving armoured protection.