I struggled upright again, so I could see what was happening. Rozalia had aimed for the mouth of another tunnel, wider and taller than the ones connecting the vaults together. We reached it after a few more minutes of driving, during which the shaking had still not shown any signs of abating. As we got closer I saw there was a slope, leading upwards, and I felt almost giddy with joy. We passed beneath an archway, the EV bouncing hard as it hit a sudden, sharp incline.

The incline got steeper, and I started to wonder if the tunnel would never end. Then I caught sight of a circle of stars directly ahead, and growing nearer by the second. Dust and debris fell all around us, small boulders and rocks falling from the rough-hewn ceiling and rolling down the steep incline towards us. Rozalia swerved around them with remarkable expertise. Then the circle of stars expanded, and we were back out on the surface, just a few miles from where I had first entered the Icelandic Retreat with Nadia.

I stared at the landscape around us, which had become completely transformed in just a few hours. In the distance, Hekla spewed dust and flames high into the airless sky, while rivers of fire, stark against the unending black night, spread all around us.

‘Tell me again it won’t be like this every time,’ I said, gripping the back of the passenger seat.

‘Oh, honey,’ said Rozalia with a savage grin. ‘Don’t listen to her. That was just for starters.’

Thirty minutes later, we were back in the Reykjavik Forward Base for the first time since that morning. The base consisted of a single, large pressurized dome with a drive-in airlock garage, located in the centre of what had once been a park on the outskirts of Reykjavik.

Most of the interior of the dome was taken up by a single transfer stage. The rest of the place had already been stripped of all its equipment and supplies. By the time the five of us emerged from the garage, there were a few soldiers left, hurriedly wheeling the last remaining crates of equipment onto the stage. The rest of the staff had all gone.

‘You’re alive?’ one of the soldiers exclaimed in shock.

‘Don’t look so surprised,’ said Nadia, pulling off her helmet. ‘What’s happening? Has everyone else transferred back across?’

The soldier nodded. ‘They have. We’re the last to go. I . . . ought to give you a heads up. The Commander’s pretty pissed at you people.’

‘Barnes?’ asked Nadia, and the man nodded. ‘Why?’

‘You disobeyed his orders,’ the soldier replied.

‘Who gives a shit?’ Nadia barked. ‘We saved a whole EV full of people, didn’t we?’

Rozalia came up beside Nadia and took the woman’s hand in her own. ‘Now’s not the time, Nads,’ she said softly.

Nadia looked at her uncertainly.