Dalip scrubbed at his eyes, which felt like they were full of grit. Work hard, the bullet-headed East European had said. He knew how to do that. He’d done nothing but, even though it was a different sort of work to this. He recognised that he should be curled in a little ball in the corner somewhere, mind numb, but instead, despite being out of breath, in pain, half-roasted, barely able to see or speak, he was unnaturally calm. Presumably, the shock would hit later, when he was back home, sitting at the kitchen table with his mum and dad and a cup of tea.

‘Okay,’ he said, ‘Can we get out of here?’ He put the back of his hand on the door they’d come through, and jerked it away. Too hot.

‘I believe so. We must find the exit.’ Stanislav shone his torch at the remaining door, opened it and peered through.

The next room was dominated by a tall case, also spray-painted in the same grey colour. Beyond that, another door, a narrow corridor, and suddenly the space opened out. Their torch beams picked out a broad junction, and an arrow on the wall – a modern one, with a stylised symbol of a running figure heading through an opening. When they investigated, they found stairs going up.

‘Up is good, right?’ Dalip stood at the bottom of the steps: at the top, the corridor appeared to turn to go back over the tracks.

‘Up is the only way, whether it is good or not. Come.’

Stanislav walked carefully up the broad stairs, torch beam scanning ahead. Dense white smoke curled in the curved roof space and reached tendrils down towards them. He crouched to keep his head out of the worst of it, and Dalip ducked down, too.

The portion of the corridor that bridged the rail track below was melting. The floor seethed and swam, and the tiles that had clung to the walls throughout the Blitz were spalling off, cracking and falling into the slurry below.

‘That way is out. It may take our weight, it may not. It may kill us anyway.’ Stanislav spat on to the ground, and it hissed. ‘Who goes first?’

Dalip wanted to nominate himself. The bridge wasn’t going to last. If he didn’t go now, he’d not do it at all.

‘Together.’

They ran through the molten bitumen, side by side, sending up splashes of black liquid. Their thick overalls helped protect them from the worst, even though the distance was something they might have jumped if they’d had clearer heads and more time.

They were out and through, and in the darkness and smoke, it was easy to miss that the corridor turned sharp left. There was suddenly a wall rearing up at them, and a moment’s confusion as they swung their torches to see which way to go.