‘Whenever the TARDIS passes within a few star systems of the Quantum Anvil, I can feel it in my bones. On occasion, I’ve even navigated by it.’ The Doctor nodded grimly. ‘If this device ever malfunctions, it will corrupt huge tracts of space-time. I check in on it every now and again, just to make sure that it isn’t leaking.’

In normal circumstances Ace would have been frustrated at that revelation, annoyed with him for pretending that their landing here was purely random, but she was certain now that she could see dark, sinuous shapes weaving at the edges of the light which were somehow mesmerising.

With the Doctor now totally focused on the readings on the console, Ace stepped closer to the Anvil to get a clearer look at the strange phenomenon. As she did so, another series of tremors shook the building, much larger than the previous ones.

Dust and grit rained down from the domed ceiling, and the ground heaved beneath her feet. Ace threw up her hands to steady herself.

And her arm slipped inside the column of energy.

Time stopped.

For the briefest fraction of a second Ace felt she could see everything – literally everything – from the tiniest microbe to the largest supermassive black hole, all overlaid. The sensory input was so great, so overwhelming that she could barely endure it. A gasp of pain and helplessness burst from her lips as she felt her mind and body shutting down at the onslaught on her senses.

Mercifully the vision ceased as suddenly as it had started and Ace found herself drifting through the memories of a baby – warm and calm and safe. Without knowing how, Ace knew that these were memories of being in the womb.

There was a sudden burst of light and pain and time started to speed up again, racing through the life of the child as she grew from baby to toddler to teenager. With a jolt of surprise, Ace realised that it was her own life she was witnessing – no, not just witnessing, reliving. She winced as the tide of memories washed over her: every school lesson, every fight with Mum, every friendship, every kiss, every betrayal, every regret.

Swamped with conflicting emotions, she tried to pull back, but the Anvil had her in its grasp, and it wasn’t finished with her yet.

With shocking suddenness, the bombardment of remembrance ceased and she found herself face to face with a female figure, her face hidden in shadow. Already knowing what would happen, Ace raised her hand in greeting and the figure standing in front of her did the same. This was no image in a mirror; the Anvil was showing her herself, as she was here and now.

Abruptly the figure shattered, fragmenting and reforming into multiple Aces – two, then four, then eight, then sixteen … The Anvil was extrapolating every possible path that she could take from this point in space and time.