Subsequently, he learned that his name had been put forward by a Dutch scientist, a visiting fellow at Tehran University, who sometimes sat and talked to Marvar in the canteen.

‘You may accept.’ It was clear that many consultations had taken place before his head of department summoned Marvar and gave him this news in a calm, dispassionate voice, and then the conditions. His wife had to stay behind, he had to report back on his own research every month, he was to avoid making contacts outside his team at the Clarendon. If anyone questioned him, he was to represent himself as a single father. The West was full of them.

It was Shula who had decided. An opportunity to work in Oxford – it was not likely to come again, and Samir would benefit; the government had consented to pay for his schooling.

‘She said to me: “No question, Rustum, you have to go.”’

Father and son had arrived in England soon after the signing of the international treaty that suspended Iran’s nuclear programme in exchange for sanctions relief. A thirty-year stand-off – three decades of ‘mutual demonisation’ – had come to an end. Tensions relaxed further as Iran began again to export oil. Marvar received no more instructions. He lived with Samir in digs in Merton Street. He got on with his work. He ate takeaways; he never went to parties. Last summer, he’d flown with Samir to Tehran to visit Shula, by then six months pregnant. Marvar was back in Oxford when Jamileh was born three months later. He had been looking forward to seeing his baby daughter for the first time in March, at the annual meeting of the Iranian Atomic Energy Organisation.

‘But these last weeks – the atmosphere has changed utterly.’ America’s threat of sanctions had sent the Iranian authorities berserk, he said. ‘Every day, they issue new orders to those who have dealings with the West. At the same time, they are arresting people.’

Marvar’s research at the Clarendon now obsessed them. They insisted that he report back not every month, but every week, in detail. That was not all.

‘I’m not a spy – no, no, you mustn’t think that. But my people are very suspicious, you cannot believe how suspicious. They have made other conditions. They want to make me into a spy.’

He spoke in a low voice as if petrified of being overheard. ‘I have to report on the rest of the team. If they are not satisfied with … I can’t think straight.’

His pace had faltered. He needed to swallow before he could go on. With an unexpected sob, he said: ‘I have heard from my cousin that Shula has been taken away.’

In his large brown abstracted eyes was the horror of a man who might never see his wife again. Rejas had shown the same anguish when talking about Yolanda.