'A plesiosaur,' said Kin. 'All wrong for this stratum, but what the hell.' The camera floated over the half excavated skeleton, focusing now on the distorted rectangles by its side. Kin nodded. Now it was quite clear. The beast had been holding a placard. She could just make out the wording.

' "End Nuclear Testing Now",' she said levelly.

It must have taken a lot of work. Weeks, probably, and then a very complicated program to be fed into the machine's main brain.

'How did you find out?' asked the girl.

Because there was a telltale built into every machine, but that was an official secret. It was welded into the ten-kilometre output slot to detect little unofficial personal touches, like pacifist dinosaurs and mammoths with hearing aids -- and it stayed there until it found one. Because sooner or later everyone did it. Because every novice planetary designer with an ounce of talent felt like a king atop the dream-device that was a strata machine, and sooner or later yielded to the delicious temptation to pop the skulls of future palaeontologists. Sometimes the Company fired them, sometimes the Company promoted them.

'I'm a witch,' she said. 'Now, I take it you admit this?'

'Yarss,' said Hendry. 'But may I make, uh, a plea in mitigation?'

He reached into his tunic and brought out a book, its spine worn with use. He ran his thumb down it until the flickering pages stopped at his reference.

'Uh, this is one of the authorities on planetary engineering,' he said. 'May I go ahead?'

'Be my guest.'

'Well, uh. "Finally, a planet is not a world. Planet? A ball of rock. World? A four-dimensional wonder. On a world there must be mysterious mountains. Let there be bottomless lakes peopled with antique monsters. Let there be strange footprints in high snowfields, green ruins in endless jungles, bells beneath the sea; echo valleys and cities of gold. This is the yeast in the planetary crust, without which the imagination of men will not rise."