‘I can tell you for free, you’re still being sour.’ Then she burst out laughing. A breath of wind through the window blew away the top page of the test paper lying on the tea table, exposing the question. Huang Yiyi was clearly transfixed by the equations set out there, and glancing at me she asked, ‘Is this what you’re working on?’

‘No, it’s for the person I’m here to find to work out.’

‘So that’s the test?’

‘Yes.’

‘Can I look?’

Before I had even agreed, she had picked it up and started reading.

I smiled coldly. ‘Laughing and joking won’t help you with this one …’

She didn’t pay any attention to me; it was as if she were quite alone. She was muttering to herself: ‘It’s a mathematical puzzle … someone’s gone to a lot of trouble to make this look complicated … whoever came up with this is not entirely psychologically normal …’ She seemed almost to be sleepwalking, and then she suddenly sat down, her lips moving silently. She seemed half awake and half dreaming. I had been startled by the sudden change: one moment she was laughing, the next she was in a world of her own, but without any obvious transition. It was as if there was a switch somewhere, which allowed her to change personality at will.

After a short time spent in a daze, she suddenly came to herself again, and raising her head she said, ‘I can solve this equation, but it’s going to take a bit of time. Can I take it away with me, or do you want me to work here?’ I told her she could take it away, and found another copy of the question paper to give her. She picked it up and walked out, still somewhat disorientated. She seemed to be a completely different person from the one who had first entered my room.

I showed her out and, struck by her dazed look, I felt like a sleepwalker myself.

8

I was sleepwalking.

About half an hour later I heard the sound of her footsteps in the corridor, coming towards my room. The footsteps stopped when they got to my door, but there was no sound of knocking. Instead I saw that something was being pushed under the door. When I picked it up, I saw it was an answer paper, and a note. At the top of the note she had drawn a really cute cartoon of me instead of addressing me directly, and below she had written: