The Doctor blinked to find herself in a kind of airlock with a further heavy, bronze door in front of her. ‘Deadlocked,’ she deduced, and looked down at Squidget. It threw out its trademark tendrils once more and, like a master safe-cracker, seemed to listen to the tiniest sounds coming from the lock. This took longer, and the Doctor was trying not to pace with impatience. But eventually the second door opened onto a small chamber containing a third. The Doctor could feel an increasing heaviness in the atmosphere, the hairs on the back of her neck standing on end. She knew she was drawing closer to incredible energies.

Squidget helped her open the third door and finally they were through.

A blaze of bright light blew into her face and the Doctor realized at once that she had reached the inner sanctum of whatever force was at work here. There were no details to the room; it was all glowing white, an ’80s pop video of a place, gloss and shine but no coherent depth. Perspective changed with every look you took. The Doctor perceived menace bristling at the fringes of her sight, just outside her focus, but more worryingly she could sense a puncture in the reality of the room: a quantum borehole right through the space-time vortex …

‘Professor …!’

Ace’s voice burst from nowhere and roiled around the space and no-space of the chamber. The Doctor looked around, frantic. ‘Ace?’

‘Professor, please …’

‘I’m here for you. I’m going to find you, all right?’ The Doctor knew where Ace was; the only place she could be. The same place she had helped push Ace into once before.

Ace was inside the endless prison of the Wraiths. Inside the Quantum Anvil. In those creatures’ hands.

‘And I can’t get in. Can’t get to you.’ The Doctor looked down at Squidget. ‘Or can I?’ She waved the sonic, scanning for the precise entry point. ‘Squidge, you can meld incompatible tech together, mechanical or otherwise. If you could link me to the quantum borehole, destabilise my own physical form long enough for me to survive a journey inside and get Ace back out …?’

Squidget strained eagerly like a greyhound spotting a hare.

‘Find me the interface,’ the Doctor breathed. ‘Find me the way in.’ She set Squidget down and it wiggled, metal widgets probing the air. With a beep, it sent out a probe which seemed to disappear like a fishing line into water.

‘Got it!’ The Doctor clapped. ‘Good boy. Clever boy!’ She strode up to Squidget. ‘Now if you can connect me to—’

Suddenly Squidget screamed as the air itself turned against it, spinning it round and lifting it up. Blue flame burst from its side and it shrivelled like a balloon.

‘Squidge!’ the Doctor shouted.

But Squidget was already gone, sucked inside the borehole like water down a drain.