‘You think my father was among them?’ She shook her head, staring at the coins, at their inscriptions. ‘Who knows this?’

‘It’s not a secret,’ he said. ‘Not with a capital “S”. But it’s not common knowledge, either.’ His lips were dry and he moistened them with his tongue. ‘They were vetted, of course, to make sure they weren’t still active Nazis, and some of them were given alibis.’ She was listening hard, her forehead creasing, taking in what he was telling her, making sense of it.

‘Why?’ she said.

‘There was a race to develop the A-bomb.’ She nodded. ‘The big fear was that the Germans had already developed it, or were damn close to developing it.’

‘I didn’t know that,’ she said.

‘It turned out that the Allies were more advanced than the Germans on the A-bomb,’ he said. ‘Or the Americans, at least, as we learned in Hiroshima and Nagasaki. But the Germans were more advanced in their delivery systems. They didn’t need bombers. They could send weapons on rockets. Ballistics. The Russians were way behind both.’

‘And Hermann Fischer?’

‘He came to work on ballistic missiles.’ He paused. ‘De Havilland was a cover. He commuted from Hatfield to a secret location in Buckinghamshire where he and a bunch of other German scientists used their expertise to work on rockets and guided missiles.’ He shouldn’t be telling her this, could be had under the Official Secrets Act, but she had to know.

‘The Brits and Americans agreed that the Americans would develop the Intercontinental Ballistic Missiles,’ he went on. ‘And we would focus on the Intermediate Range Ballistic Missiles. All the more urgent now, after Sputnik.’

She stood nodding, silently.

‘De Havilland are building the rocket,’ John went on. ‘And Hermann Fischer, Arnold Fisher, is the principal scientist responsible for its production.’

She said nothing, but he saw her swallowing, again and again.

‘My father.’ She walked out of the room and he followed her. There was a stone bench, and she sat down.

‘How do you know this?’ she said. ‘Who are you? Some kind of spy?’

‘When I was in Berlin my job was to translate,’ he said. ‘I was there when they interviewed the scientists.’

‘Did you interview him?’ She twisted on the bench, searching his face.

‘I may have done,’ he said. ‘I can’t remember. We interviewed so many.’

She breathed in deep. ‘Are you sure?’ she said. ‘Are you sure it’s the same person?’

‘Yes.’

She turned to face him once more, her face flushed, lips twisted. ‘He lied. He lied.’ She stood up, slinging her bag over her shoulder. He held her arm, gripping it hard as she winced.

‘Bette.’ He used her German name. ‘There is more. Lass’ mich bitte ausreden. You must hear me out.’