He pointed to the shaft. ‘When the escapees came over, an electric winch was used to haul them up. We’ve put down a ladder. It’s been secured but, if you wish to go down, it’s at your own risk.’

The group took turns with the embassy wives going first. One or two found the ladder tricky. They returned to the surface looking both shell-shocked and in the grip of an excitement that they tried to tamp down. Laure and Petr went last.

‘The rule was absolute silence whilst either digging or escaping,’ said their guide, warming to his subject. ‘Voices carry from underground. And, of course, there was no question of using explosives to make the work progress quicker.’

The descent was tricky and, with each step down, the air grew more rank. Petr went first and held out his hand to help Laure down the final rungs but she refused it. To access the tunnel proper, it would be necessary to drop down flat and to edge forward on the stomach, which was not advised as water had pooled on the beaten earth floor.

‘Anatomie’s hit “Tunnelling”,’ said Petr. ‘I think it was banned.’

She did not blink. ‘You know it was.’

‘Whose song was it?’

She took a while to reply. ‘Tomas’s.’

A couple of electric lights had been rigged up, which had been switched on. Petr crouched down and peered along the long and dark stretch. It did not look big enough even for a slim person to force themselves through but, in flight, people achieved the impossible.

‘They build their tunnels in underground cities to outwit the winter,’ went the lyric of the song.

If he remembered correctly.

Hot air flowed over his face, smelling of decay from hidden miasmic rot. It was all he could do not to retch.

Laure hunkered down beside him. She took one breath and clapped her hand to her nose. ‘Oh God, to think of them nose to tail…’ her voice was muffled. ‘Probably terrified. Pushed on by adrenaline. The guide says that a baby was brought through.’

He swallowed the saliva swilling around his mouth. ‘Not sure I could have done it.’

‘You didn’t have to.’

She wasn’t being malicious, merely matter-of-fact, but the remark caught him on the raw. ‘Is that why you got me here? To make the point? Or to punish me?’

They were almost pressed together. He could feel her warmth and smell her floral scent. History and politics made for hard taskmasters – something which he had always known – but it had never been brought home so cruelly that their divisions deformed love and compassion. And, almost certainly, understanding.

They also made yearning for someone on the other side a sharp and thankless experience.