Marvar was watching Samir in the act of taking a corner kick when his mind made an acrobatic skip: what if you could find a way of producing an utterly symmetrical implosion from a spherical laser?

It blasted him in the face. The match was still going on when he hurried from the pitch and tore back to the Clarendon.

Over the next days, he didn’t stop making calculations, on paper napkins, the backs of menus, yellow post-it notes (‘now I know what they’re called’) – ‘in sandpits even!’

What he had realised: size didn’t matter. The machine didn’t need an elaborate magnetic cage, it didn’t need to be enormous, it didn’t have to be like Wembley. ‘It could be no bigger than a football.’

The audacity of it. His idea went against the received wisdom of every internationally known scientist. But he couldn’t breathe a word to Samir, whose kick had inspired it. He couldn’t log on to his computer, it was likely to be monitored, and so he entered his calculations into a notebook that he kept in his coat. It was vital that nobody suspected what he was working on. Marvar’s team believed him still to be plugging away at plasma focus, and so he continued to conduct experiments with a tungsten-tipped electrode, making careful records, but these experiments were a decoy. He devoted the rest of his time to creating his ‘football’.

‘For three weeks, I hardly left the lab. The materials were all there, I didn’t need much.’

He slaved through the night; there was less risk of being interrupted or observed. He tested a number of lasing mediums before fixing on the one which worked: ‘It was silly of me not to have thought of it sooner, a nonlinear optical crystal that I’d experimented with in Tehran.’

Marvar had constructed a blanket out of this to wrap around the hot plasma, using the blanket as a laser. ‘I’m making it sound simple. It wasn’t simple.’ The uniform thickness of the blanket was critical. ‘To achieve the smooth wavefront, I had to mix in other lasing materials as well.’

‘Go slow, please,’ said Dyer. ‘What other materials?’

Marvar reeled them off. (On struggling next morning to remember the details of their conversation, Dyer had a burn of regret that he hadn’t reached into Marvar’s pocket and borrowed his notebook. In his hangover, he was unable to recall if Marvar had said neodymium or monazite or bastnasite, or any of the candidates that Dyer googled. What he did grasp: Marvar had found a way of doping sand from rare earths to make crystals which, when added to the principal lasing medium, smoothed out all instabilities and dramatically increased the neutron production.)