Gilles replaced the salt cellar. He stretched out his right hand, and one by one bent back the fingers. ‘The truth is, I don’t have any more idea than you. But I would like to find out. Believe me, Jean, I would like to find out.’

He was not going to insult Dyer by beating around the bush. Friends in the intelligence community, whose investments he looked after, had alerted Gilles to the possibility that Marvar had in his possession information that could benefit Gilles – benefit them all, if Marvar was alive.

‘Business respects no borders, any more than GCHQ.’

The irresistible rumour swirling through safe rooms from Millbank to Riyadh: an unknown young Iranian physicist at the Clarendon had conducted an experiment which stood to recast the future of energy.

‘The dinner party you came to with Miranda. Remember Ralph Cubbage? Well, after you had gone he stayed on, I naturally assumed for my fine old Cuban rum, but no, it was to tell me a story that I found most interesting. I would be curious, Jean, to know if you think it as interesting as I do.’

The incident which Cubbage described had taken place on the day of the Asselins’ dinner party, early in the morning. ‘He couldn’t get it out of his mind,’ Gilles said.

As was his energetic habit, Cubbage had arrived first thing at the Clarendon. He unlocked the door into the laboratory, and immediately was on the alert. ‘It was obvious to his vigilant eyes that someone had carried out an experiment, and left in a hurry.’

Strange particles of sand in the target chamber. A single loose zirconium sample – tiny, white – staring up from the concrete floor.

‘Even as Ralph retrieves the sample, his suspicion is falling on which one of the eight has dropped it. The night before, Professor Whitton had treated the team to dinner at the Magdalen Arms, but the student from Tehran had excused himself.

‘Ralph logs in to the cameras, and sees that they were last operated at 7.32 the previous evening. The details are important.

‘But here’s the intriguing thing. The experimental data has been removed from both.

‘He is suspicious. He switches on the new neutron activation detector, installed at considerable expense only in January, thanks to a last-minute donation from Berkeley. Ralph had set the biometric access code himself, shortly after his arrival here – he has not a big amount of faith in the Clarendon’s security, he tells me.

‘The results are so strange that he examines the system logs. They show a denied attempt to delete files. The unauthorised user did not possess the administrator privilege to do this.

‘I think we can picture the intruder’s face. Unshaven, panicked – pushing buttons, keys, frenetic to cover up records of his test. Ray’s first thought: “He’s jammed the motherboard – that’s why he took off.” But sorry, it’s not jammed.