'The answer will come to you.' The Doctor looked up for the first time, and smiled past her. 'When you've lived a few hundred years, come back and I'll tell you if you've got it.'

'Thanks,' she muttered.

'Oh, please, don't worry.' The Doctor removed two printed circuit-boards and started rummaging in his pockets for the right tool. 'Age, you know, is more than just a shrinking of the skin on the skull, more than your hair falling out and your teeth going brittle. It's a slow, painful process. And on the way you find out what people were talking about all along.' He produced the probe he had been looking for, and beamed at her. 'You can't do a crash course in Time.'

Benny stood up, smoothing down her jeans. 'I'll be in the games room.'

The Doctor waved in acknowledgement. He was intent on the circuit-boards.

She turned to go.

'Happy Birthday,' he added.

Benny smiled wearily. 'You shouldn't have,' she told him, and left the console room with the book tucked into her pocket.

When she had gone, his face changed its expression very slightly. It was like the rippling of a flag in the breeze. When you're around, he thought, I feel uncertain, I lose sight of the plans I've made.

He let the circuit-boards from the TARDIS console fall from his hand and they hit the floor with a crash. The Doctor waited a few seconds to make sure Benny didn't come running back. Then he looked sadly down at the discarded circuits.

'Reconfiguration,' he said to himself. 'Dynamic forces of change.' He looked up at the softly glowing roundels of the console room just for a moment, remembering the confusion of the past few days. He nodded. 'But for whom?'

He knew the TARDIS would not answer.

'You know what I'm doing,' he said. 'I hope.'

When his foot stamped down on the two circuit-boards, the dozens of pieces skidded outwards like smashed pieces of nutshell, hitting all four walls of the console room before coming to rest.

Epilogue.

Output In the darkened, timeless room, the pendulum was still swinging, dripping condensation from its icy surface. Inside, something fluttered, stirred in agitation.

The prisoner was confused. It was being given conflicting information now in the data-rods which prodded it from all sides.

Thinking that this was a moment of weakness for its captor's powers, it rocked the sphere, straining again to escape. Fleeting images appeared against the surface one could perhaps have been a screaming mouth, another might have been a large hand, its print outlined in condensation. But they lasted about as long as pictures in flurries of snowflakes.

Data was rushing through the attachments, bombarding the prisoner. And once again it heard that hateful echo, the voice of the being who had led it into a trap and now used it for manipulation of Time.

'An interesting experiment, don't you think?'

The prisoner, blind to anything but its own desire for escape, screeched soundlessly. It wanted no more. The energy it was using up was squeezing the life from its tired form.

'Oh, come now. Where's your scientific curiosity? Your race is meant to be intelligent, after all. Didn't you enjoy watching the Gavond gaining power... growing... Yes, yes, I know the Doctor knocked everything back into shape again, but he was never meant to lose. Oh, no, that wasn't the point at all.' The captor chuckled again. 'The experiment showed exactly what it was meant to show. That within parameters, time can be changed. You and I, my friend, we made incursions into the fabric of the real universe this time...'

Trepidation seized the prisoner. It was clear that the ordeal was not going to be over yet.

It strained, with its failing faculties, to make out the other being's words. As if the captor knew how exhausted it felt, there came new, painful, invigorating pulses which wrenched its body, forced it to listen to the next words, which it heard with astonished clarity.

'The second phase is finished. It's time for something completely different.'