‘Exactly,’ Lyang said. ‘It can happen. Sometimes an irrelevant is accidentally known to them. Usually they are given a list of things in advance, so that if they might be shown something they recognise it can be changed before the actual test. That wouldn’t have been done for the demo.’
Li was shaking his head, baffled. ‘So how could Lynn Pan possibly tell from any of these responses that somebody was lying? I mean, lying about what? Lying how? All they were doing was looking at pictures.’
‘Wait a minute, wait a minute,’ Margaret said suddenly. She looked at Li. ‘You remember Mei Yuan’s riddle?’ He looked at her blankly. ‘The one about the two deaf mutes in the paddy field.’
Li blinked in surprise. ‘So she tried that one out on you after all.’
But Margaret wasn’t listening. Her mind was racing off on lateral planes. ‘Each of them thought he was left in that field on his own,’ she said. ‘And that the other one had sneaked off with the food or the drink to keep it for themselves.’
‘You’ve lost me,’ Lyang said, looking from one to the other through a haze of fatigue.
So Margaret told her the riddle, but didn’t wait for her to work it out. ‘It was dark,’ she said. ‘That’s why they couldn’t see one another. They were both there, and neither of them was lying about it. They were both telling the truth, but they just didn’t know it.’
‘You’ve lost me now, too,’ Li said.
Margaret was searching for a way to unfuzz her mind, to express herself clearly. She waved a hand at the computer. ‘This MERMER thing. It can’t tell if you’re lying, right? Your brain sees something it recognises, it makes an involuntary response. You record it right there on the graph, and it’s plain for everyone to see. You see something you don’t recognise, you have no response. That’s also on the graph. So it’s got nothing to do with lying. But it’s got everything to do with telling the truth.’
They were both looking at her, concentrating hard, waiting, still not getting it.
‘Don’t you see? You can’t help but tell the truth, because you have no control over how your brain responds. Lynn Pan must have known there were anomalies in the irrelevants. But that’s neither here nor there. If you have a MERMER response to something you’re not supposed to, well that’s just a measure of the imperfect conditions in which the test was being conducted. But if you don’t have a MERMER response to something you should have, then that’s weird. That’s really off the wall. That doesn’t make any sense at all.’
Light began to dawn in Li’s eyes. ‘It’s one of the targets,’ Li said. ‘He didn’t recognise something he should have.’ Then he frowned. ‘What the hell could that be?’
Lyang said, ‘Well, we only have to look at nine photographs in relation to the graph to find out.’
She went into the Graphs D folder and double-clicked on the first of the graph icons, and the MRM software decoded the document. A window opened up on the computer screen showing a jagged graph line running from left to right. Using the mouse to capture the scroll bar at the bottom of the window enabled Lyang to scroll through the length of the graph. Its peaks and troughs related to a bar running along the top of the screen which held tiny icons of the images being shown at that moment to the testee. Each image was labelled probe, target, or irrelevant. So it was a simple matter to compare the graph responses to the target pictures, while enabling them to ignore the other forty-five.
Li focused all his attention on the graph. The MERMER responses, indicating knowledge or recognition, were represented by distinctive peaks that stood out well above the average flat response. The tiny icons of the photographic images were hard to make out. Li saw a car, but it just looked like any other ministerial car. No doubt Subject D, as Hart had called him, would have recognised its number plate. He saw the pink and white ministerial apartments where he had called on Commissioner Zhu first thing the previous morning. But there was nothing in that to give away the identity of Subject D. All five of the senior officers who had taken part in the demonstration with Li that day would have apartments in those blocks. Only Li, as by far the most junior officer, was allocated an apartment in the ministry compound. There was a picture of a young man in his late teens or early twenties. A son, perhaps. Li did not recognise him. There was a photograph of the exterior of a restaurant. It was not one Li knew. A favourite eatery, perhaps. Another showed the main entrance of Beijing Police Headquarters in East Qianmen Avenue. Any one of them would have recognised that one. Infuriatingly, there was nothing that indicated to Li the identity of Subject D.
Lyang suddenly stopped scrolling. ‘There,’ she said. And she pointed at the screen, almost triumphantly. She had followed in the footsteps of her dead husband and found what he found. ‘No MERMER.’ The graph showed a flat response to a picture clearly labelled target, where there should have been a MERMER response.
‘What is it?’ Margaret squinted at the picture, but it was too small to be identifiable.
Lyang double-clicked on the icon and the photograph opened up on top of the graph to reveal an orange sky at sunset, framed by the branches of trees drawing the eyes toward two serrated towers in silhouette rising against gold-edged clouds.
‘What’s that?’ Margaret asked.
Li frowned. ‘I’ve no idea. Looks like a couple of pagodas.’
‘It’s the Double-pagoda Temple,’ Lyang said, taking them by surprise, and they looked at her to see tears making slow tracks down her cheeks. ‘Also called the Yongzuo Temple. I only know because when he first came here, Bill did the whole tourist bit. Dragged me round every tower and palace and tourist attraction in Beijing. And then we did trips. Overnights to places like Xian and Taiyuan.’ She nodded toward the screen and wiped away the tears with the back of her hand. ‘Which is where that is.’ She forced a smile. ‘It was typical of Bill. He knew more about China than the Chinese. The twin towers of the Double-pagoda Temple are the symbol of Taiyuan. But if you don’t come from there you probably don’t know that.’
Margaret said, ‘Well Subject D certainly didn’t.’ She shrugged. ‘But I don’t see the significance of it. Why were they showing it to him in the first place?’
Li slapped his hand on the desk. ‘It has to be his home town,’ he said. ‘It’s the only category of the nine target pictures that it would fit. They showed all of us pictures of our home towns.’
Margaret ran her hand back through tangled, tousy hair. ‘But why wouldn’t he recognise his home town? I mean, if those pagodas are the symbol of the place…’
Li sat staring into space, his brain working overtime. Finally he said, ‘There can only be one reason he didn’t recognise it.’ He looked at Margaret. ‘It’s not his home town.’
She frowned. ‘You mean they made a mistake?’
‘No. I mean he’s not who he says he is.’
Margaret threw her hands out in despair. ‘And we don’t even know who he’s supposed to be.’
Li pressed fingers into his temple, screwing up his eyes in concentration, trying to get his mind to focus. ‘That doesn’t matter,’ he said. ‘We can find that out easily enough now.’ He was thinking back to the MERMER test itself. Lynn Pan had shown Li a list of his target pictures. He knew he was going to see a picture of his home town in Sichuan. She must have shown the man who killed her a similar list. And he must have known that he wouldn’t recognise the place that was his home town. Even before she showed him it. And there was nothing he could do about that. His brain would respond in a way over which he had no control. It would tell her the truth, and reveal his lie. She must have known instantly that there was something far wrong. And he must have been watching for it, knowing she would see it, and planning how he would get rid of her even before the test was over.