Cracking another country’s cipher is basically a plot, a dark conspiracy – it is an undercover fight to the death between two countries, or between two political systems. At that time the situation with Taiwan was already so tense that war could break out at any moment, and so cracking RECOVERY was being pushed to the top of the agenda. It was top secret and there was no margin for error: even the slightest rumour leaking out would put us in an extremely disadvantageous situation and might even bring about the failure of our ‘counter-RECOVERY’ operation; and that would threaten the security of New China. Basically nothing about this operation could leak out. If there was a leak it couldn’t come from me, or my life would be ruined. It was that way of thinking, that kind of concern that meant that before I left I had made special arrangements to maintain the secrecy of my mission, spreading a layer of concealing powder on my letter.

The concealing powder had to be laid down in conditions where oxygen and moisture had been eliminated, because when it came into contact with them it vanished into smoke, just like snow melting in the sun. As all concealment was stripped away, my secret mission became black ink on white paper, and I looked straight at the Party secretary. I noticed that he suddenly became very solemn. Then he asked me how many people I wanted. I held up one finger.

‘One.’

‘One? But … what are your specifications?’ he asked me suspiciously.

‘First,’ I said, ‘it must be a mathematician with a record of independent research.’

He fished out a pen and made a note, murmuring under his breath: ‘It must be a mathematician; that’s number one.’

‘Secondly,’ I said, ‘it must be someone who understands Russian, preferably someone who has studied there.’

‘Understands Russian, preferably having studied in the Soviet Union …’

‘Thirdly, the person must have absolutely no political problems.’

‘That’s the third point; what is the fourth?’

‘We don’t want someone too old – preferably middle-aged or younger, and single is best.’

‘That’s the fourth point; what is the fifth?’

‘There isn’t one,’ I said.

‘Is that it?’

‘That’s it.’

‘One person, who answers your four specifications.’

‘Yes. The first three specifications are the important ones. We don’t want many people – in fact, the fewer the better, and ideally only one. This isn’t an ordinary battle where the side with the biggest battalions wins. This is one mathematician deconstructing another mathematician’s meticulously created maze; both the mathematician who creates the maze and the one who deconstructs it must be very special; able to leap mountains in a single bound. That’s the kind of person we are looking for, and I hope you can suggest some suitable candidates.’

‘How many do you want?’

‘How many have you got?’

‘Maybe a dozen or so.’

‘Let me see them,’ I said.

‘When?’