Tilo laughed. ‘No. And you can’t hear the mountain, can you?’

That was when Mount Perfect exploded.

Tilo told me later that, if I’d known where and how to look, I could have seen the north side of the mountain bulging out. The immense chthonic defect had been growing visibly, at a metre a day. Well, I didn’t notice that. Thanks to some trick of acoustics I didn’t even hear the eruption - though it was heard by other Navy teams working hundreds of kilometres away.

But the aftermath was clear enough. With Lian and Doel, and with Academician Tilo limping after us, I ran to the crest of a ridge to see down the length of the valley.

As we watched, a billion tonnes of rock slid into the valley in a monstrous landslide. Already a huge grey thunderhead of smoke and ash was rearing up to the murky sky. A sharp earthquake had caused the mountain’s swollen flank to shear and fall away.

But that was only the start of the sequence of geological events, for the removal of all that weight was like opening a pressurised can. The mountain erupted - not upwards, but sideways, like the blast of an immense weapon, a volley of superheated gas and pulverised rock. The eruption quickly overtook the landslide, and I saw it demolish trees, imports from distant Earth, sentinels centuries old flattened like straws. I was stupefied by the scale of it all.

And there was more to come. From out of the ripped-open side of the mountain, a chthonic blood oozed, yellow-grey, viscous, steaming hot. It began to flow down the mountainside, spilling into rain-cut valleys.

‘That’s a lahar,’ Tilo murmured. ‘Mud. The heat is melting the permafrost - the mountain was snow-covered two weeks ago; did you know that? - making up a thick mixture of volcanic debris and meltwater. I’ve learned a lot of esoteric geology here, Lieutenant.’

‘So it’s just mud,’ said Lian uncertainly.

‘Just mud. You aren’t an earthworm, are you, marine?’

‘Look at the logging camp,’ Doel said.

Already the mud had overwhelmed the heavy equipment, big yellow tractors and huge cables and chains used for hauling logs, crumpling it all like paper. Piles of sawn logs were spilled, immense wooden beams shoved downstream effortlessly. The mud, grey and yellow, was steaming, oddly like curdled milk.

Just mud. For the first time I began to consider the contingency that we might not get out of here.

In which case my primary mission was to preserve Tilo’s data. I quickly used my suit to establish an uplink. We were able to access Tilo’s records, stored in cranial implants, and fire them up to the Spline. But in case it didn’t work—

‘Tell me about dark matter,’ I said. ‘Quickly.’

Tilo pointed up at the sky. ‘That star - the natural sun, the dwarf - shouldn’t exist.’

‘What?’