By now, the vault was incandescently bright with lava. More and more of it came pouring in behind us, and showed absolutely no signs of abating. It had melted the frozen air that lay on every surface, filling the vault with dense clouds of gas and dust that pooled beneath the ceiling and reduced visibility to nearly zero. It took an effort to keep my focus as I studied the spread-out sheets.

I came back up beside her, but could see nothing through the windscreen – not even the far wall of the vault, although I knew we were rapidly approaching it.

‘Where are they?’ I asked, looking over at Nadia.

‘In the next vault after this one,’ Nadia replied. ‘There’s a connecting tunnel, if I remember the map. We should be able to just drive straight thr—Oh shit.’

Before I could ask her what the problem was, I looked back up and saw the fog had cleared sufficiently to reveal both the far wall and the connecting tunnel directly before us. The tunnel entrance, however, had become partly blocked by rubble – heavy girders from an adjacent construction project had collapsed across its entrance in a great pile. I knew immediately there was no way the EV was going to be able to get past such an obstruction.

‘Is there enough space we can at least walk through?’ I asked in desperation. Blocked or not, there were gaps through which I could see into the darkness of the next vault. Even if the EV couldn’t get past the wreckage, it didn’t mean we couldn’t.

‘I guess,’ said Nadia, pressing a button next to the microphone. ‘Rozalia, can you still hear me?’

‘Loud and clear, sweetheart,’ said a woman’s voice. ‘What the hell’s going on back there? There’s all that light and—’

‘Hekla’s erupting,’ said Nadia. ‘A lava flow’s flooding the first vault.’ She pulled to a halt as near the mess of collapsed girders as she dared. ‘It looks like we’re going to have to come through to your side on foot.’

‘You shouldn’t have come, Nads,’ said the woman’s voice. ‘There were some real bad tremors down here and the EV went into a ditch and we’ve been stuck here ever since.’

‘Anyone else with you?’

‘Two Authority scientists I was escorting.’

‘What about your towline?’ asked Nadia. ‘Did you try using that to get you out?’

‘We tried. We got the winch running, but it got damaged when we crashed. It’s not strong enough to pull us back out of the hole we’re in.’

I could just make out a glint of silver in the next vault that might have been the other EV.

‘Are they just on the other side of the tunnel?’ I asked Nadia. ‘I thought I could see them.’

‘Yeah, they are. Why?’