For the next several minutes, I followed Mr Lin all around the building. Despite his age, my host showed little sign of infirmity; he carried his bulk steadily, if slowly, hardly ever pausing for breath. I pursued his dark gown and whispering slippers up and down narrow stairs, and along back corridors lit often only by a single lantern. He led me through areas that were bare and cobwebbed, past numerous neatly stacked wooden crates of rice wine. Elsewhere the house became sumptuous; there were beautiful screens and wall hangings, clusters of porcelain displayed within alcoves. Every so often, he would open a door, then stand back to let me pass. I entered various kinds of room, but – for some time at least – saw nothing at all familiar to me.

Then finally I stepped through a door and felt something tugging at my memory. It took a few seconds more, but I then recognised with a wave of emotion our old ‘library’. It had been greatly altered: the ceiling was much higher, a wall had been knocked through to make the space L-shaped; and where there had once been double doors through into our dining room, there was now a partition against which were stacked more crates of rice wine. But it was unmistakably the same room where as a child I had done much of my homework.

I drifted further into the room, looking all around me. After a while I became aware of Mr Lin regarding me and gave him a self-conscious smile. At which point, he said:

‘No doubt much has been changed. Please accept my apologies. But you must understand, over eighteen years, which is how long we have lived here, a few alterations have been inevitable to meet the needs of my household and of my business. And I understand the occupants before us, and those before them, carried out extensive alterations. Most unfortunate, my good sir, but I suppose few could have foreseen that one day you and your parents …’

He trailed off, perhaps because he thought I was not listening, perhaps because like most Chinese, he was uncomfortable with apologies. I went on gazing about me for a while longer, then asked him:

‘So this house, it's no longer owned by Morganbrook and Byatt?’

He looked astonished, then laughed. ‘Sir, I am the owner of this house.’

I saw I had insulted him, and said hurriedly: ‘Yes, of course. I do beg your pardon.’

‘Don't worry, my good sir’ – his genial smile had quickly returned – ‘it was not an unreasonable question. After all, when you and your dear parents lived here, that was no doubt the situation. But I believe that has long ceased to be. My good sir, if you will only consider how much Shanghai has changed over the years. Everything, everything has changed and changed again. All this’ – he sighed and gestured about us – ‘by comparison these are small changes. There are parts of this city I once knew so well, places I would walk every day, I now go there and I know not which way to turn. Change, change all the time. And now the Japanese, they wish to make their changes here. The most terrible changes may yet overtake us. But one must not be pessimistic.’

For a moment, we both stood there in silence, continuing to look about us. Then he said quietly:

‘My family, of course, will be saddened to leave this house. My father died here. Two grandchildren were born here. But when my wife spoke earlier – and you must forgive her frankness, Mr Banks – she did speak for us all. We will consider it a great honour and privilege to return this house to you and your parents. Now, my good sir, let us continue if we may.’

I believe it was not long after that we climbed a carpeted staircase – one which certainly did not exist in my time – and stepped into a luxuriously furbished bedroom. There were rich fabrics, and lanterns casting a reddish glow.

‘My wife's room,’ Mr Lin said.

I could see it was a sanctuary, a cosy boudoir where the old lady probably whiled away most of her day. In the warm lantern light, I could make out a card table upon which a number of different sorts of game appeared to be in progress; a writing desk with a column of tiny gold-tasselled drawers running down one side; a large four-poster bed with layers of veil-like drapes. Elsewhere my gaze caught various fine ornaments, and items of amusement whose exact natures I could not guess.

‘Madame must like this room,’ I said eventually. ‘I can see her world here.’

‘It suits her. But you mustn't concern yourself on her behalf, my good sir. We will find her another room she will come to love equally.’

He had spoken to reassure me, but something fragile had entered his voice. He now drifted further into the room, over to a dressing table, and became absorbed by some small object there – perhaps a brooch. After several moments, he said quietly:

‘She was very beautiful when she was younger. The most beautiful flower, my good sir. You cannot imagine. In this respect, I am like a Westerner in my heart. I have never wanted any wife but her. One wife, quite enough. Of course, I took others. I am Chinese, after all, even if I have lived all my life here in the foreigners’ city. I felt obliged to take other wives. But she is the one I truly cared for. The others have all gone now, and she is left. I miss the others, but I'm glad, in my heart I'm glad that in our old age, it is just the two of us again.’ For a few seconds, he seemed to forget my presence. Then he turned to me and said: ‘This room. I wonder how you will come to use it. Pardon me, this is very impertinent. But do you think this room will be for your own good wife? Of course, I am aware that for many foreigners, however wealthy, husband and wife will share the same room. I wonder then if this room will go to yourself and your good wife. My curiosity, I realise, is most impertinent. But this room is very special for me. It is my hope that you will put it to special use.’

‘Yes …’ I looked around it again carefully. Then I said: ‘Perhaps not my wife. My wife, you see, to speak frankly …’ I realised that in this talk of a wife, I had had a picture of Sarah in my mind. Covering my embarrassment, I went on quickly: ‘What I mean, sir, is I'm not yet married. I have no wife. But I think this room will suit my mother.’

‘Ah yes. After all the inconveniences she has had to suffer, this room will be ideal for her. And your father? I wonder, will he share it with her in the Western manner? Please forgive my great intrusion.’

‘It's no intrusion, Mr Lin. After all, by letting me in here, it is you who have allowed me great intimacy. You have every right to ask these questions. It's just that this is all rather sudden, and I've not yet had time fully to make my plans …’

I drifted into silence and went on gazing at the room. Then after a moment, I said to him: ‘Mr Lin, I'm afraid this may upset you. But you've been more open and generous than I could ever have expected, and I feel you deserve my honesty. You said yourself just now, how inevitable it is that a house undergoes alteration whenever its occupants change. Well, sir, dear as these rooms are to you, I'm afraid that once my family are again living here, we will carry out our own alterations. This room too, I fear, will change beyond recognition.’

Mr Lin closed his eyes, and there was a heavy silence. I wondered if he would become angry, and for a second regretted being so honest with him. But then when he opened his eyes again, he was regarding me gently.

‘Of course,’ he said, ‘it is quite natural. You will wish to restore this house to just the way it was when you were a boy. That is quite natural. My good sir, I understand it perfectly.’

I thought about this for a moment, then said: ‘Well, actually, Mr Lin, we would probably not turn it back exactly to what it was then. For one thing, as I remember it, there were many things we were unhappy about. My mother, for instance, never had her own study. With all her campaign work, a little bureau in the bedroom was never adequate. My father too wanted a little workshop for his woodwork. What I'm saying is that there's no need to turn back the clock just for the sake of it.’

‘That is most wise, Mr Banks. And although you have not yet taken a wife, perhaps soon there will come the day when you have the needs of a wife and children to consider.’

‘That's certainly possible. Unfortunately, just at present, this question of a wife, in my case, Western customs notwithstanding …’ I became very confused and stopped. But the old man nodded sagely, saying:

‘Of course, in matters of the heart, things are never simple.’ Then he asked: ‘You wish for children, good sir? I wonder how many you will have.’

‘As a matter of fact, I already have a child. A young girl. Though she isn't really my daughter as such. She was an orphan and now she's in my care. I do look on her as a daughter.’

I had not thought about Jennifer for some time, and mentioning her like this so unexpectedly caused a powerful feeling to well up within me. Images of her ran through my mind; I thought of her at her school, and wondered how she was, and what she had been doing that day.

I perhaps turned away to hide my emotions. In any case, when I next looked at him, Mr Lin was nodding again.

‘We Chinese are well used to such arrangements,’ he said. ‘Blood is important. But so is household. My father took in an orphan girl and she grew up with us as though she were my sister. I regarded her as such, though I knew always of her origins. When she died, in the cholera epidemic when I was still a young man, I felt as much grief as when my blood sisters passed away.’

‘If I may say so, Mr Lin, it's a great pleasure to talk to you. It's rare to find someone so immediately understanding.’

He gave a small bow, bringing his fingertips together before him. ‘When one has lived as long as I have, and through the turmoil of these years, one knows many joys and sadnesses. I hope your adopted daughter will be happy here. I wonder which room you will give her. But of course, forgive me! As you say, you will alter.’

‘In fact, one of the rooms we saw earlier would be ideal for Jennifer. It had a little wooden ledge running along the wall.’

‘She likes such a ledge?’

‘Yes. For her things. And in fact there's one further person I shall be accommodating here in this house. I suppose she was officially a sort of servant, but in our household she was always much more. Her name is Mei Li.’

‘She was your amah, good sir?’

I nodded. ‘She would be older now and I'm sure she'd appreciate a rest from her work. Children can be very taxing. It was always my intention that when she was old, she'd go on living with us here.’

‘That is most kind-hearted of you. One so often hears of foreign families who throw out the amah once her charges are grown. Such women are often to be seen ending their days as street beggars.’

I gave a laugh. ‘I hardly think that could ever happen to Mei Li. In fact, the very thought is quite absurd. In any case, as I say, she'll be living here with us. As soon as my task is accomplished, I'll turn my mind to locating her. I don't imagine it will be so difficult.’

‘And tell me, good sir, will you give her a room in the servants’ quarters or with the family?’

‘With the family, certainly. My parents might take a dim view of that. But then really, I'm the head of the household now.’

Mr Lin smiled. ‘According to your custom, that will certainly be so. For us Chinese, fortunately for me, the old are permitted to go on ruling the house well into their foolish years.’

The old man laughed to himself and turned towards the door. I was about to follow, but just at that moment – quite suddenly and very vividly – I found another memory returning to me. I have thought about it since, and I have no idea why it was that particular recollection rather than any other. It was of an occasion when I was six or seven, when my mother and I had raced each other along a stretch of lawn. I do not know where exactly this was; I would suppose now we were in one of the parks – perhaps Jessfield Park – for I can remember a trellised fence beside where we ran, covered in climbing flowers and creepers. It was a warm day, but not especially sunny. I had impulsively challenged my mother to the race, to some marker a short distance before us, as a way of showing off to her my improved running ability. I had assumed completely that I would outpace her, and that she would then express, in her usual way, her delighted surprise at this latest manifestation of my maturing prowess. But to my annoyance she had kept up with me all the way, laughing as she went, although I was running with all my strength. I do not remember which of us actually ‘won’, but I still recall my fury at her, and my sense that I had suffered a grave injustice. It was this incident that came back to me that night as I stood in the snugly sheltered atmosphere of Madam Lin's bedroom. Or rather, a fragment of it: a memory of me pushing into the wind with all my might; my mother's laughing presence beside me; the rustling of her skirt, and my rising frustration.

‘Sir,’ I said to my host, ‘I wonder if I may ask you. You say you've lived all your life here in the Settlement. I wonder then if during that time you ever met my mother.’

‘I never had the good fortune to meet her in person,’ Mr Lin said. ‘But of course, I knew of her, and of her great campaign. I admired her, like all decent-minded people. I am sure she is a fine lady. And I've heard it said she is very beautiful.’

‘I suppose she might be. One never thinks about whether one's mother is beautiful.’

‘Oh, I've heard it said she is the most beautiful Englishwoman in Shanghai.’

‘I suppose she might be. But of course, she'll be older now.’

‘Certain kinds of beauty never fade. My wife’ – he gestured at the room – ‘she is as beautiful to me now as the day I married her.’

When he said this, I suddenly felt as though I were intruding, and this time it was I who made the first move to leave.

I do not remember a great deal more about my visit to the house that evening. Perhaps we stayed another hour, talking and eating with the family around the table. In any case, I know I parted from the Lin family on the best of terms. It was during the journey back, however, that Morgan and I rather fell out.

It was probably my fault. I was by that stage tired and somewhat overwrought. We had been travelling through the night for a while in silence, and my mind had perhaps begun to drift back to the immense task before me. For I remember I said to Morgan, quite out of the blue:

‘Look, you've been here a few years now. Tell me, have you come across a certain Inspector Kung?’

‘Inspector Kung? Policeman or something?’

‘When I was a child here, Inspector Kung was something of a legend. As a matter of fact, he was the officer originally in charge of my parents’ case.’

To my surprise, I heard Morgan beside me give a guffaw. Then he said:

‘Kung? Old Man Kung? Yes, of course, he used to be a police inspector. Well then, it's no wonder nothing got sorted out at the time.’

His tone took me aback, and I said rather coldly: ‘In those days, Inspector Kung was the most revered detective in Shanghai, if not the whole of China.’

‘Well, he still has something of a name for himself, I can tell you. Old Man Kung. Well I never.’

‘I'm glad at least to hear he's still in the city. Do you have any idea where I'd find him?’

‘Simplest way's just to wander around Frenchtown any night after dark. Bound to come across him sooner or later. You usually see him in a heap on the pavement. Or if he's been let into some hole of a bar, he'll be snoring away in a dark corner.’

‘Are you implying Inspector Kung's become a drunk?’

‘Drink. Opium. Usual Chinaman stuff. But he's a character. Tells stories about his glory days and people give him coins.’

‘I think you're thinking of the wrong man, old fellow.’

‘Don't think so, old chap. Old Man Kung. So he really was a policeman. I always fancied he was making all that up. Most of his stories are preposterous. What's the matter, old fellow?’

‘The trouble with you, Morgan, is you keep muddling things. First you muddle up me and Bigglesworth. Now you get Inspector Kung muddled with some worthless ragamuffin. Being out here's got your head all soft, old man.’

‘Now look here, pipe down a bit. What I'm telling you, you'll hear from anyone else you care to ask. And I rather take exception to your comments. Nothing soft about my head.’

We may have returned to slightly more civil terms by the time he dropped me off at the Cathay, but our parting was distinctly cold and I have not seen Morgan again since. As for Inspector Kung, it had been my intention after that evening to seek him out without delay, but for whatever reason – perhaps I feared Morgan might have been telling the truth – I have never made it a priority – at least, not until yesterday, when my search through the police archives threw up the inspector's name again in the most dramatic fashion.

This morning, incidentally, when I mentioned Inspector Kung in passing to MacDonald, his reaction was not dissimilar to Morgan's that night, and I suspect here was yet another reason for my impatience with MacDonald as we faced each other in his airless little office overlooking the consulate grounds. All the same, with a little more effort, I know I could have made a much better job of it. My central error this morning was to allow him to goad me into losing my temper. At one point, I fear, I was practically shouting at him.

‘Mr MacDonald, it simply isn't enough to leave things to what you insist on calling my “powers”! I have no such “powers”! I am a mere mortal, and I can only achieve my goals if I am given the sort of basic assistance that allows me to go about my work. I've not asked much of you, sir. Hardly anything at all! And what I've asked, I've put to you very clearly. I wish to speak to this communist informer. Just speak with him, a short interview will suffice. I made this request to you in the clearest terms. I fail to understand why arrangements still have not been made. Why is that, sir? Why is that? What can possibly be impeding you?’

‘But look here, old fellow, this is hardly a matter for my office. If you wish, I'll get the police commissioner over to see you. Mind you, even then, you see, I'm not at all sure you'll get anywhere useful. It's not they who have the Yellow Snake …’

‘I fully appreciate it's the Chinese government who are keeping the Yellow Snake under their protection. That is why I have come to you and not to the police. I'm aware that in a matter of this magnitude, the police are an irrelevance.’

‘I'll see what I can do, old chap. But you must understand, this isn't a British colony. We can't go ordering the Chinese about. But I'll talk to someone in the appropriate office. Don't bet on anything happening too quickly though. Chiang Kai-shek's had informers before, but never one with quite such extensive knowledge of the Reds’ network. Chiang would lose a good few battles with the Japs before allowing anything to happen to this Yellow Snake chap. As far as Chiang is concerned, you see, the real enemy's not the Japs but the Reds.’

I gave a loud sigh. ‘Mr MacDonald, I do not care about Chiang Kai-shek or his priorities. Just now, I have a case to solve, and I would like you to do whatever you can to secure an interview for me with this informer. I am putting it to you personally, and if all my efforts come to nothing because this simple request is not granted, I shan't hesitate to let it be known that it was you I came to …’

‘Now really, old fellow, please! There's no need to take this sort of line! No need at all! We're all friends here. We all wish you to succeed. Take my word for it, we really do. Look here, I've said I'll do all I can. I'll talk to a few people, you know, people in that line of work. I'll talk to them, tell them how strongly you feel. But you have to understand, there's only so much we can do with the Chinese.’ Then he leant forward and said confidingly: ‘You know, you might try the French. They have a lot of little understandings with Chiang. You know, of the off-the-record sort. The kind of thing we wouldn't touch. That's the French for you.’

Perhaps there is something in MacDonald's suggestion. Perhaps I might indeed get some useful help from the French authorities. But frankly, since this morning, I have not given this option much thought. It is clear to me that MacDonald, for reasons which as yet remain unclear, is prevaricating, and that once he has recognised the overwhelming importance of granting my request, he will do whatever is necessary. Unfortunately, it is probable I handled this morning's meeting so incompetently I will have to tackle him one further time. It is not a prospect to which I particularly look forward, but at least the next time my approach will be different, and he will not find it so easy to send me away empty-handed.