The Snowmen, the human label for the vanished builders of this lacy monster, had an utterly alien motivation. The Snowmen decided that to record events - and only to record - was the highest calling of life. They took apart their world and rebuilt it as a monstrous data storage system. After that they watched time unravel - and waited for the universe to cool, so they could capture even more data.

Thus the Snowflake had hung in space for thirteen billion years. Then, during the Assimilation, a human ship came.

The Navy crew, intent on plunder, had been unsubtle - but their ship had been devastated by an unexpected blow, broken apart by a beam of directed gravity waves.

It had taken some time to work out what had happened, how the Snowflake had struck back.

Mela lacked the vocabulary to express the concepts downloading into her mind, and she looked at the Curator. Reluctantly, he closed his eyes, and began to speak deliberately. ‘There is a profound principle at work. Once it was known as the Mach principle. Mach, Marque, something like that. Every particle in the universe is linked to every other. That is why inertia exists; when you push something, the universe itself drags it back.’

Symat frowned. ‘What connections? Gravity?’

The Curator frowned. ‘That, and quantum wave functions, and, and - I can see it, I can’t say it! The ancients understood. If you use complex arithmetic to extend most theories of cosmology—’

Symat held up his hand. ‘Just tell me what happened.’

‘The Snowmen had a defensive system. They found a way of manipulating these cosmic linkages. A way to use them as a weapon.’

Symat barely understood enough to be amazed. ‘How?’

‘Does it matter? I guess you learn a lot in thirteen billion years.’

Thanks to its Mach-principle weapon the Snowflake was saved from the Assimilators, that first time. But the humans returned, of course, evaded the weapon, and took what they wanted. They used the technology of the Snowflake itself in their own information-storage systems across the Galaxy.

And they took away the strange global-manipulation weapons system, but that turned out to be much harder to understand. When it didn’t yield early results it was reduced in priority, shuffled from one research centre to another, until it became so obscure, despite its potency, that a clique of undying were able to spirit it away and develop it for their own purposes.

The Curator peered at Saturn uneasily. ‘And that, it seems, is what is held under those clouds. A weapon of last resort.’

‘But,’ said Symat, ‘what has this got to do with me?’

Suddenly Mela’s face worked, and the tone of her voice hoarsened. ‘We need you because the Guardians won’t listen to us. Is that clear enough for you?’

Symat was shocked. This time the intervention was crude, as if she had been possessed by a different personality altogether.