I found this out by chance when the support for my washbasin broke and the whole thing would no longer stand up properly. I went to the carpentry shed to ask for a nail, and came across the master carpenter, Comrade Zhang, who was cutting holes in a piece of wood. Beside him there was a hand-drawn plan for something that looked a bit like an adding machine, with measurements. I thought that it looked like Huang Yiyi’s handwriting, and felt curious, so I asked the carpenter and he said that Comrade Huang had asked him to make it, but he had no idea what it was for. On my way out, I noticed a pile of things in the corner, some round, some conical, some cylindrical and some spherical, and asked the carpenter what they were for. He said he had made them for Comrade Huang some time ago, but now she didn’t need them any more and had brought them back to be broken up. My interest was even more piqued – what on earth could Huang Yiyi want such bizarre objects for? All the racket from her room, was it because she was playing with them? I couldn’t see that these toys could bear any relation to the decryption of RECOVERY. Later on when Huang Yiyi explained her idea, I was very impressed. You just had to be impressed: an ordinary person is an ordinary person and a genius is a genius – if you meet one you know about it.

That day when I left the woodworkers’ shed, I found Huang Yiyi in the nearby forest. I was expecting her to be there feeding the squirrels, but instead she was standing underneath one of the trees discussing something with the madman who spent his time running around the forest. The madman raised his head to look at the treetops, or perhaps it was the sky; maybe he was talking to her, but then on the other hand maybe he wasn’t – he could easily have been talking to himself, lost in a world of his own. He was the man Huang Yiyi had asked about the first time she went to Chen’s office, the lunatic. His name was Jiang Nan, a cryptographer who had joined us at the same time as Chen, and who was eventually driven mad by decrypting PORPHORY. He knew too many secrets to be allowed to leave Unit 701 even though he was mad. We couldn’t even let him see his family, so we let him roam through the mountains, spending his days running through the forest. He had the silent trees, he had the flowers and squirrels, he had this whole beautiful, illogical world for company. If he saw a stranger he would stop them and say, ‘I cracked PORPHORY, the most difficult of all the KMT ciphers. No one else could crack it, only me …’