Physics had eluded Dyer; after maths it was his weakest subject. Not even Rougetel, fluent in the sciences as he was in the arts, could help him make better sense of it. In fission, Dyer scrambled to recall, atoms were made to split; in fusion, they were forced to merge – producing potentially immeasurably greater power. He had learned all this at the Phoenix, from a young master who couldn’t have been more than a few months out of university.

‘Everything I know about fusion,’ he told Marvar apologetically, ‘could be written on a post-it note.’

‘A post-it note?’ said Marvar, smiling almost for the first time, and then throwing back his head and bursting into laughter, after Dyer had explained what, exactly, a ‘post-it note’ was. ‘Everything I know, too!’

Marvar gestured at the grey afternoon sky. ‘To put it in one line, fusion is what is happening in the sun – if we could get to see it in Oxford – every second, every minute, every day. It’s why the stars sparkle. So why not here?’

This had been the challenge facing scientists for eighty years, the holiest of grails. If we could replicate on earth the processes of the sun and the stars, then in a flash our energy problems, global warming, would be sorted. For ever!

But how?

He was looking at Dyer with incredibly tense eyes. ‘Well, it can be done,’ and gave a distressingly pinched laugh. ‘I have found a way.’

It was Dyer’s turn to burst out laughing. But he corrected himself when he saw Marvar’s face, and he did not question a word of it by the time that Marvar had finished talking.

Marvar’s mood had shifted, his tempo had quickened. Once he began, he did not stop. Every sentence he spoke made him need to speak another. Before, he had sounded furred, tense, but now, with no one to overhear him save for Dyer, he spoke clearly, coherently, as if in a confessional.

Marvar unlatched the gate into Port Meadow and for the next ninety minutes gave an impassioned account of his recent research at the Clarendon. The large meadow stretched flat to the river, unploughed for millennia, a grazing pampa for cattle and horses. From across it, they would have seemed like two academics deep in talk, one of them engrossing the other in his subject – the history of our future energy.

Chapter Eleven

‘IF YOU HEAT SOMETHING REALLY HOT,’ said Marvar as they walked towards the weir, ‘it goes ballistic. It’s like shutting a kid with tantrums in a cage – like shutting Vasily in a cage.’ Dyer had to think of Vasily as a plasma. ‘When you heat plasma, it doesn’t like it. It goes whistling around, creating instabilities, and takes on a mean-minded identity of its own.’