He rang off. ‘Friend Cubbage,’ he explained. ‘The Americans want to grill Professor Whitton.’ Dyer did not need to know this; even so, out of some residual sentiment, Updark had confided in him.

‘It was Cubbage who overruled Whitton, as no doubt you’ve guessed. Cubbage is adamant that information recorded by the Clarendon’s cutting-edge new detector can’t be faked, any more than it can be deleted – which is what Marvar, I’m told, tried to do.’

Dyer waited to see if he was going to say more. ‘Could the Americans have information they’re not sharing?’

Updark twisted his face. ‘There is one respect in which America has changed since the 1950s. They have a great deal of trouble keeping anything secret. Their national character is to tell you everything they know. My overriding impression is that the Americans are still as much in the dark as we are about if, or how, Marvar might have achieved fusion, and also about where he might be even as we speak.’

Updark slid the phone back into his jacket and from the same pocket brought out his spiral notebook and opened it.

‘Oh, I wanted to ask you about this.’

He read out: ‘“Ordinarily he took the train.” Now what does that sentence mean? Hissop reckons it might be a code.’

This revelation confirmed what Dyer suspected. While he was eating Lorna’s flapjacks in Eynsham, Updark’s men had indeed been searching his house. But could it have been them also who seized the decoy that Dyer had planted in the green folder? About this, he was still undecided.

Updark looked fully at Dyer with his cold eyes. ‘Why are you smiling?’

‘It was a dream I had.’

‘A dream,’ Updark nodded. ‘A dream,’ he repeated, as if in another context he might like how it sounded.

Dyer gave him a nudge. ‘Come on, Lionel, you must have had dreams when you imagine you’ve been given the answer to everything. I woke myself up and wrote it down. As you see, it was pitiful nonsense.’ Like the formula based on Basil Bunting’s poem ‘Chomei at Toyama’. And Dyer allows himself another smile. To picture Updark, Hissop and Lorna, that roomful of code-people, crowded around a screen, their frowns.

The muscles in Updark’s jaw relax. ‘Speaking of dreams. That Russian mother, Katya. See much of her, do you? I gather your sons have got over their spat.’

‘They have. And no, I don’t see much of her.’