Volodya had an unnerving sense that the rigid system of hierarchy and deference that sustained Soviet Communism was beginning to weaken and disintegrate.

They found the barricade party just where the building administrator had predicted. Volodya got out of the car, told the driver to wait, and studied the work.

A main road was strewn with anti-tank ‘hedgehogs’. A hedgehog consisted of three pieces of steel railway track, each a yard long, welded together at their centres, forming an asterisk that stood on three feet and stuck three arms up. Apparently they wreaked havoc with caterpillar tracks.

Behind the hedgehog field an anti-tank ditch was being dug with pickaxes and shovels, and beyond that a sandbag wall was going up, with gaps for defenders to shoot through. A narrow zigzag path had been left between the obstacles so that the road could continue to be used by Muscovites until the Germans arrived.

Almost all the workers digging and building were women.

Volodya found Zoya beside a sand mountain, filling sacks with a shovel. For a minute he watched her from a distance. She wore a dirty coat, woollen mittens and felt boots. Her blonde hair was pulled back and covered with a colourless rag tied under her chin. Her face was smeared with mud, but she still looked sexy. She wielded the shovel in a steady rhythm, working efficiently. Then the supervisor blew a whistle and work stopped.

Zoya sat on a stack of sandbags and took from her coat pocket a small packet wrapped in newspaper. Volodya sat beside her and said: ‘You could have got exemption from this work.’

‘It’s my city,’ she said. ‘Why wouldn’t I help to defend it?’

‘So you’re not fleeing to the east.’

‘I’m not running away from the motherfucking Nazis.’

Her vehemence surprised him. ‘Plenty of people are.’

‘I know. I thought you’d be long gone.’

‘You have a low opinion of me. You think I belong to a selfish elite.’

She shrugged. ‘Those who are able to save themselves generally do.’

‘Well, you’re wrong. All my family are still here in Moscow.’

‘Perhaps I misjudged you. Would you like a pancake?’ She opened her packet to reveal four pale-coloured patties wrapped in cabbage leaves. ‘Try one.’

He accepted and took a bite. It was not very tasty. ‘What is it?’

‘Potato peelings. You can get a bucketful free at the back door of any Party canteen or officers’ mess. You mince them small in the kitchen grinder, boil them until they’re soft, mix them with a little flour and milk, add salt if you’ve got any, and fry them in lard.’

‘I didn’t know you were so badly off,’ he said, feeling embarrassed. ‘You can always get a meal at our place, you know.’

‘Thank you. What brings you here?’

‘A question. What is isotope separation by gaseous diffusion?’

She stared at him. ‘Oh, my God – what’s happened?’

‘Nothing has happened. I’m simply trying to evaluate some dubious information.’

‘Are we building a fission bomb at last?’