‘You may not be aware of it,’ he said, ‘but the information that you sent back over the years has been very useful in cracking a number of high-level military ciphers used by enemy powers including the Americans, the British and the Taiwanese. As a result, people at headquarters have come to rely on your intelligence, and several senior officers were most unhappy about the decision to recall you, seeing how well you were doing over there.’

‘It would be difficult to carry on, given current conditions,’ I said. ‘Recently they put me under a lot of restrictions – much worse than before.’

‘Yes, things really aren’t going too well.’ Then he asked me what I thought the prospects were like for Sino-Soviet relations.

I said, not good.

‘You’re right. Of course, something that is bad for us is good for other people. I don’t know whether you have seen it, but the Hong Kong newspapers say that Chiang Kai-shek is getting ready to celebrate his eightieth birthday in Nanjing.’

‘He can say whatever he likes; he’s just running off at the mouth.’

‘Two years ago he was just running off at the mouth, but this time he is definitely up to something. You’ve been away, so you don’t really understand that we’re in terrible trouble right now. We’ve had natural disasters for the last couple of years, and now in addition to the prospect of a Sino-Soviet split there is also tension on the border between China and India. It’s just been one damn thing after another. We’re in trouble, and he’s going to take advantage of that. That’s Chiang Kai-shek’s plan, the bastard.’

‘Ten years ago, when the Korean War had just broken out, didn’t he try to take advantage? He sent bombers over every day and wave after wave of special agents, thinking that he could launch a double-pronged attack on the Mainland. And what happened? It didn’t work and he practically bankrupted himself.’

‘History is repeating itself; the only thing that’s changed is the slogan. At that time they talked about “Invading the Mainland”; now it’s “Recover the Mainland”. Anyway, they have stopped using PORPHORY and switched to a new cipher called RECOVERY.’

I knew that PORPHORY was the high-level cipher that the Taiwanese used to communicate with their agents on the Mainland, which an American expert had created for them. It was reckoned to be secure for twenty years, and so far it had been in use for a decade. We had started to make some headway in cracking it in the last two years, but we were still a long way from the stage where they would have to change it. To suddenly switch to this new cipher suggested that they might well be getting ready to go to war.

‘So who gets the job of cracking it?’ I asked.

‘Your old home: Unit 701.’