‘If he is on the run, then he’d better clean his rear mirror,’ said Hissop in the same bleak tone. ‘There are a lot of people who won’t rest till he’s told them what he knows – or else he’s chopped up in bags in their freezer, to borrow a phrase. And I mean a lot.’

‘Before we get into that,’ said Updark, ‘I still haven’t formed a clear picture of the man. Roly?’

‘“Rude, sarcastic, touchy, withdrawn, monosyllabic,”’ Hissop read from a page clipped to his board. ‘But also: “Smart, loyal, witty, patriotic, creative, deft.”’

Updark turned to Dyer. ‘How did he impress you?’

‘I barely knew him, as I keep saying. But if you want me to add to your list, I’d say honest, sensitive, confused, frightened, and, as I told you, physically out of shape.’

‘Not a rabble-rouser then?’

‘I wouldn’t have thought so, no.’

Updark sighed. ‘Show him, Roly.’

Hissop unclipped a photograph and handed it to Dyer.

The colours had faded, but Marvar could be seen clearly. Much younger, leaner, his features sharpened by a moustache, like a leftist student. He was marching in a crowd down a foreign street under a blue sky. He held up a placard and his mouth was open as if he were shouting something.

Dyer smiled.

Updark studied him. ‘Did he tell you he was an activist? No, I don’t suppose he did.’

‘If he was an activist,’ said Dyer, who all at once could picture Marvar fired up – by Heisenberg, by Houtermans, by the regime’s treatment of his mother – ‘then I’m sure it was for democracy.’

‘Did he tell you that he studied engineering before he switched to physics?’

‘He did not.’

‘Well, let’s put aside for the moment that most jihadis have engineering backgrounds. Let’s also agree that he was demonstrating for democracy, and that he is every one of those things you say he is, and he was not sent as a spy by the regime to continue research that would benefit them. Let’s further assume that since leaving Iran he has become a really good mechanical engineer as well as a plasma physicist, and that he has by some extraordinary and unanticipated miracle done what we think. But here I come to something that puzzles me. No one else rates him so highly. Not here, not in Tehran, not anywhere. The man who wants to crack fusion has to take a pretty big size in hats. From whichever angle you view it, Rustum Marvar’s head doesn’t fit.’

Hissop nodded. ‘Frankly, he was below our radar.’

‘Not only our radar.’ Updark glanced at Dyer. ‘I’m only telling you what my people tell me. Your friend Rustum is not exactly high up in the pecking order of brilliant Iranian scientists. The chief nuclear negotiator has never heard of him. Same in Oxford.’