They walked through the long, narrow park. On one side was a busy road. All along the other side, the towers of the Kremlin loomed over a high wall. ‘To look at it, you’d think our leaders in there were being held prisoner by the Russian people,’ Volodya said.

‘Yes,’ Zoya agreed. ‘Instead of the other way round.’

He looked behind them, but no one had heard. All the same it was foolhardy to talk like that. ‘No wonder my father thinks you’re dangerous.’

‘I used to think you were like your father.’

‘I wish I was. He’s a hero. He stormed the Winter Palace! I don’t suppose I’ll ever change the course of history.’

‘Oh, I know, but he’s so narrow-minded and conservative. You’re not like that.’

Volodya thought he was pretty much like his father, but he was not going to argue.

‘Are you free this evening?’ she said. ‘I’d like to cook for you.’

‘You bet!’ She had never invited him to her place.

‘I’ve got a piece of steak.’

‘Great!’ Good beef was a treat even in Volodya’s privileged home.

‘And the Kovalevs are out of town.’

That was even better news. Like many Muscovites, Zoya lived in someone else’s apartment. She had two rooms and shared the kitchen and bathroom with another scientist, Dr Kovalev, and his wife and child. But the Kovalevs had gone away, so Zoya and Volodya would have the place to themselves. His pulse quickened. ‘Should I bring my toothbrush?’ he said.

She gave him an enigmatic smile and did not answer the question.

They left the park and crossed the road to a restaurant. Many were closed, but the city centre was full of offices whose workers had to eat lunch somewhere, and a few cafés and bars survived.

Grigori Peshkov was at a pavement table. There were better restaurants inside the Kremlin, but he liked to be seen in places used by ordinary Russians. He wanted to show that he was not above the common people just because he wore a general’s uniform. All the same, he had chosen a table well away from the rest, so that he could not be overheard.

He disapproved of Zoya, but he was not immune to her enchantment, and he stood up and kissed her on both cheeks.

They ordered potato pancakes and beer. The only alternatives were pickled herrings and vodka.

‘Today I am not going to speak to you about nuclear physics, General,’ said Zoya. ‘Please take it as read that I still believe everything I said last time we talked about the subject. I don’t want to bore you.’

‘That’s a relief,’ he said.

She laughed, showing white teeth. ‘Instead, you can tell me how much longer we will be at war.’

Volodya shook his head in mock despair. She always had to challenge his father. If she had not been a beautiful young woman, Grigori would have had her arrested long ago.

‘The Nazis are beaten, but they won’t admit it,’ Grigori said.