Stitched into the collar was a label that Dyer hadn’t noticed before. It showed a red egret and a word in Farsi – the name of a master tailor off Laleh-zar Street, Marvar explained. ‘He warned her that Oxford is exceedingly damp.’

Smiling, Dyer went to hang it up again.

Leandro was at a sleepover with Samir. They could drink. They could talk. Marvar could decide what he was going to do.

He heard a chair groan as Marvar sat down.

Coming back into the kitchen, Dyer flapped open a cardboard box and pulled out a bottle, showing it. ‘I’ve only got white.’

‘I’ll drink white wine.’

‘I’ll put it in the freezer.’

‘Don’t worry, I’ll have it warm.’ He looked at the label. He was not reading it.

Dyer poured the glasses.

Marvar picked up his. He drank as if warm white wine and he were made for each other.

‘Who else knows about your discovery?’ asked Dyer, sitting down.

‘Just you. You’re the only one.’

Marvar had dismantled his spherical laser. But it was easy to make another – if you knew how, if you had the formula. You only needed the formula.

‘Where’s that? On your laptop?’

‘Don’t worry, it’s safe. I’m not so foolish.’ He would never risk putting anything on a computer. Every Tom, Dick, and Ralph could hack into it. Every Ayatollah too, mirthlessly.

His aversion was understandable. It made Dyer suddenly think of Rejas, who had told him how Ezequiel never wrote anything down, and neither did Socrates or Jesus. ‘The problem with text is that it assumes its own reality. It cannot answer, and it cannot explain.’

But Marvar hadn’t gone quite to that extreme. He ran a finger around the rim of his glass. ‘Know the best way to keep a secret? With a pen and paper – like in the old days. But you’re a writer,’ gesturing at Dyer’s notes and his book, still open, on the table, awaiting an inscription, ‘you know that.’

Marvar had condensed his planet-shifting invention to an algorithm on a single piece of paper. Handwritten. One copy. ‘You don’t need any other.’

That was the beauty of science, he said. It wasn’t so hard to understand as love or war. Everything could be lasered down into a few letters and numbers which you could hold in your palm.

Yet the problem remained. Who to give it to? Marvar widened his eyes, staring fiercely through his glasses at his open palm as if he would read the answer there.