‘Wrong. They’d break most known cryptography. Some algorithms would be resistant, though. But if you could solve the dihedral hidden subgroup problem, you could use quantum to break lattice-based cryptosystems.’

‘That’s not Punjabi, Baaz.’ I looked at my passport on the table. ‘It’s not even Greek to me. Give it to me in simple terms.’ I rolled my shoulders. ‘Please.’

‘Well,’ he said, scratching his head, ‘with the right algorithm, you could say that quantum isn’t the bomb – it’s all the bombs. Imagine. You could empty every bank account everywhere in the world; crack all security, access anything online, anywhere, anytime. You’d have unrestricted access to everything – from the thermostat on the fridge to the thermonuclear arsenal.’

‘Just like that? With one machine?’

‘Yes. With one machine that doesn’t exist and an algorithm that hasn’t been developed. A computer is just hardware. It won’t work without software. Like buying a PC without installing an operating system. You know, like Windows. Useless.’

‘So that’s what you’re doing? Writing an algorithm for a computer that doesn’t exist?’

He nodded again.

‘I get a grant, too. Absolute con job.’

I smiled. But rather than smiling back, Baaz suddenly looked serious again.

‘Max,’ he said, lowering his voice. ‘I have a question for you, too.’ He paused. ‘Don’t take this the wrong way … but … er, it’s just that you’ve been accused of murder and there’s a gun on my table and a bunch of commandos are after us and, well …’

‘It’s OK. Fire away.’

‘Who the fuck are you?’

I finished my tea, too, and drew breath. Under normal circumstances I wouldn’t tell him – or anyone – anything at all. Nothing true, anyway. But these were not normal circumstances.

‘I work for the British government,’ I told him. ‘Or at least, I think I still do. I was sent to do a job. It went wrong. And now, apparently, the world and his wife are after me.’

‘And “the world” is the Russians and “the wife” is your boss?’

For a twenty-something-year-old kid, he was remarkably perceptive. I pursed my lips and stared at him.

‘And?’ he asked.

‘And that’s pretty much it.’

‘No,’ said Baaz, excitement building in his voice, ‘I meant why are they after you?’

‘Good fucking question, Baaz. Good fucking question. I don’t know why.’ The billion dollars, the bad deal with Lukov … those were things definitely not to share. ‘Actually,’ I said, having an immediate half-change of heart, ‘that’s not completely true.’

I reached over and plucked the soggy hundred-dollar bill off the table and laid it out in front of him. Baaz gestured to me for permission. I nodded and he picked it up.