I spent most of the afternoon yesterday inside the dark, creaking boathouse where the three bodies had been discovered. The police respected my wish to carry out my investigations undisturbed to the extent that I lost all track of time and hardly noticed the sun setting outside. By the time I crossed the Bund and strolled down Nanking Road, the bright lights had come on and the pavements were filled with the evening crowds. After the long, dispiriting day, I felt the need to unwind a little and made my way to the corner of Nanking and Kiangse Road, to a small club I had been taken to in the days soon after my arrival. There is nothing so special about the place; it is just a quiet basement where most nights a lone French pianist will give melancholy renditions of Bizet or Gershwin. But it meets my needs well enough and I have returned there several times over these weeks. Last night, I spent perhaps an hour at a corner table, eating a little French food and making notes on what I had discovered in the boathouse, while the taxi-dancers swayed with their clients to the music.

I had climbed the staircase back up to the street intending to return to the hotel, when I happened to fall into conversation with the Russian doorman. He is some sort of count, and speaks excellent English learnt, he tells me, from his governess before the Revolution. I have got into the habit of passing a few words with him whenever I visit the club, and was doing so again last night when – I no longer remember what we were discussing – he happened to mention that Sir Cecil and Lady Medhurst had passed by earlier in the evening.

‘I suppose,’ I remarked, ‘they were off home for the night.’

At this, the count thought for a moment, then said: ‘Lucky Chance House. Yes, I believe Sir Cecil mentioned they were on their way there.’

It was not an establishment I knew, but the count proceeded without prompting to give me directions, and since it was not far, I set off towards it.

His instructions were clear enough, but I am still uncertain of my way around the side-streets off Nanking Road, and managed to get a little lost. This was not something I minded so much. The atmosphere in that part of the city is not intimidating, even after dark, and although I was accosted by the odd beggar, and at one point a drunken sailor collided with me, I found myself drifting with the night-time crowd in a mood not far from tranquillity. After the depressing work in the boathouse, it was a relief to be amidst these pleasure-seekers of every race and class; to have the smells of food and incense come wafting towards me as I passed each brightly lit doorway.

Last night, too, as I have come increasingly to do of late, I believe I looked about me, scanning the faces in the passing crowd, hoping to spot Akira. For the fact is, I had almost certainly seen my old friend shortly after my arrival in Shanghai – on my second or third night here. It was the night Mr Keswick of Jardine Matheson and some other prominent citizens had decided I should ‘taste the night-life’. I was still at that stage in something of a disorientated condition, and was finding the tour of dance-bars and clubs tiresome. We were in the entertainment area of the French Concession – I can see now my hosts were rather enjoying shocking me with some of the more lurid establishments – and we were just emerging from a club when I had seen his face go by in the crowd.

He was one of a group of Japanese men dressed in sharp suits, evidently out on the town. Of course, glimpsed so fleet-ingly – the figures had been virtually silhouettes against a row of lanterns hanging in a doorway – I could not be completely sure it was Akira. Perhaps for this reason, perhaps for some other, I did nothing to attract the attention of my old friend. This might be hard to understand, but I can only say it was so. I suppose I was assuming then there would be many more such opportunities; perhaps I felt that to meet in such a way, by chance, when we each had other companions, was inappropriate – unworthy, even, of the reunion I had anticipated for so long. In any case, I had let the moment pass, and had simply followed Mr Keswick and the others to the awaiting limousine.

Over these past weeks, however, I have had much cause to regret my inaction that evening. For although, even at the busiest times, I have persisted in searching the crowd, in streets or in hotel lobbies, as I have gone about my business, I have yet to spot him again. I am aware I could take active steps to try and locate him; but really, the case must for now take priority. And Shanghai is not such a vast place; we are sure to happen upon one another sooner or later.

But to return to the events of last night. The doorman's directions eventually brought me to a kind of square where a number of little streets intersected and the crowd was thicker than ever. There were people trying to sell things, others trying to beg, while yet others were just standing about talking and watching. A lone rickshaw that had ventured into the throng had become stuck in its midst, and as I passed, the rickshawman was arguing furiously with a bystander. I could see Lucky Chance House on the far corner, and before long was being conducted up a narrow stairway covered in scarlet plush.

I first entered a room the size of an average hotel room, where a dozen Chinese were crowded around a gaming table. When I enquired if Sir Cecil was in the building, two of the staff conferred quickly, then one of them signalled for me to follow.

I was led up another flight of stairs, along a dim corridor, then into a room filled with smoke in which a group of Frenchmen were playing cards. When I shook my head, the man shrugged and beckoned me again. In this way I soon established that the building was a gambling emporium of some size, comprising many smallish rooms, each with some game or other in progress. But I grew exasperated at the way my guide would nod knowingly each time I repeated Sarah or Sir Cecil's name, just to lead me into yet another smoky room where only the wary eyes of strangers would look up at me. In any case, the more I saw of the establishment, the more unlikely it seemed Sir Cecil would bring Sarah into such a place, and I was on the point of giving up when I stepped through a door to find Sir Cecil sitting at a table, staring at a roulette wheel.

There were as many as twenty people present, mostly men. The room was not so smoky as some others, but felt hotter. Sir Cecil was utterly absorbed and gave me only the most cursory of waves before fixing his eyes back on the wheel.

Placed around the periphery of the room were some worn armchairs covered in a reddish material. In one of these, an old Chinese man – in a Western suit and drenched in sweat – was snoring away. The only other chair occupied was in the shadowy corner furthest from the gaming table, where Sarah was resting her head on the heel of a hand, her eyes half-closed.

She gave a start when I sat down beside her. ‘Oh, Christopher. What are you doing here?’

‘I was just passing by. I'm sorry. I didn't mean to startle you.’

‘Just passing by? This place? I don't believe it. You've been pursuing us.’

We were speaking in lowered tones so as not to distract the players at the table. From somewhere in the building, I could hear faintly someone practising a trumpet.

‘I have to confess,’ I said, ‘I did happen to hear you'd come here. And since I was walking past …’

‘Oh, Christopher, you were lonely.’

‘Hardly. But I've had rather a gloomy day, and I felt like unwinding a little, that's all. Though I must admit, I'd have hesitated if I'd known you were in a place like this.’

‘Don't be cruel. Cecil and I, we enjoy being low-life. It's fun. It's all part of what Shanghai's about. Now tell me about your gloomy day. You're looking despondent. No breakthrough yet on your case, I suppose.’

‘No breakthrough, but I'm not despondent. Things are starting to take shape.’

When I then began to describe to her how I had spent over two hours on my hands and knees in a rotting boat in which three decaying corpses had been found, she pulled a face and stopped me.

‘It's all so ghastly. Someone was saying at the tennis club today, the bodies all had their arms and legs cut off. Is that true?’

‘I'm afraid so.’

She pulled another face. ‘It's too ghastly for words. But these were Chinese factory workers, weren't they? Surely, they can't have much to do with … with your parents.’

‘Actually, I believe this crime has a very significant bearing on my parents’ case.’

‘Really? They were saying at the tennis club these murders are all part of this Yellow Rat business. They're saying the victims were the Yellow Rat's nearest and dearest.’

‘Yellow Snake.’

‘Pardon?’

‘The communist informer. Yellow Snake.’

‘Oh yes. Well anyway, it's so ghastly. What are the Chinese doing, tearing at each other's throats at a time like this? You'd think the Reds and the government might put up a united front against the Japanese just for a little while at least.’

‘I suppose hatred between communists and nationalists runs pretty deep.’

‘That's what Cecil says. Oh, look at him, how can he play like that?’

I followed her gaze and saw that Sir Cecil – who had his back to us – had slumped over to one side, so that most of his weight was on the table. There seemed every possibility of his sliding off the chair altogether.

Sarah looked at me a little awkwardly. Then rising, she went over to him, placed a hand on each of his shoulders, and spoke gently into his ear. Sir Cecil came awake and glanced about him. It is possible that at this point I took my gaze off them for a second, for I am not at all certain about what exactly happened next. I saw Sarah reel back, as though she had been struck, and for a second she seemed about to lose her balance, but then recovered. Sir Cecil, when I scrutinised his back, was sitting upright again, concentrating on the game, and I could not say it was he who had caused Sarah to stumble.

She saw me staring at her, and smiling, came back and sat down beside me again.

‘He's tired,’ she said. ‘He has so much energy. But at his age, he really needs to rest more.’

‘Do the two of you often come to this place?’

She nodded. ‘And a few others very similar. Cecil doesn't much like those big glittering places. He doesn't think it's possible to come out a winner in those places.’

‘Do you always accompany him on these expeditions?’

‘Someone has to look after him. He's not a young man, you see. Oh, I don't mind it. It's rather exciting. It's what this city's all about really.’

A collective sigh went around the gaming table and the players broke into conversation. I saw Sir Cecil attempt to rise, and only then did I realise how inebriated he was. He slumped back down in the chair, but on a second attempt, managed to rise and come unsteadily towards us. I stood up, expecting to shake hands, but he rested his hand on my shoulder, as much for balance as anything else, saying:

‘My dear boy, my dear boy. Delighted to see you.’

‘Did you have any luck just now, sir?’

‘Luck? Oh no, no. Tonight's been a foul night. Whole wretched week, it's been bad, bad, bad. But you never know. I'll rise up again, ha ha! Rise from the ashes.’

Sarah too was on her feet and put out a hand to support him, but he brushed her off without looking at her. Then he said to me:

‘I say. Care for a cocktail? There's a bar downstairs.’

‘That's very kind, sir. But I really should be getting back to my hotel. Another hard day tomorrow.’

‘Good to see you're working hard. Of course, I came out here to this city wanting to sort things a little myself. But you see’ – he bent his face right down to me until it was only an inch or two away – ‘too deep for me, my boy. Too deep by far.’

‘Cecil, darling, let's go home now.’

‘Home? You call that rat-hole of a hotel home? You have an advantage on me, my dear, being the vagabond that you are. That's why you don't mind it.’

‘Let's go now, darling. I'm tired.’

‘You're tired. My little vagabond's tired. Banks, do you have a car outside?’

‘I'm afraid not. But if you like I'll try and find a taxi.’

‘Taxi? Think you're in Piccadilly? Suppose you can hail a cab out there? Just as soon cut your throat, these Chinamen.’

‘Cecil, darling, please sit down here while Christopher finds Boris.’ Then she said to me: ‘Our driver should be somewhere not far. Would you mind terribly? Poor Cecil's a little the worse for wear tonight.’

Doing my best to look good-humoured, I made my way out of the building, making a mental note of how to return to the room. The square outside was as dense as ever with people, but a little further on I could see a street in which rickshaws and motor cars were waiting in rows. I made my way over, and after a while of going from car to car uttering Sir Cecil's name at chauffeurs of varying nationalities, I eventually got a response.

When I returned to the gambling house, Sarah and Sir Cecil were already outside. She was supporting him with both her hands, but his tall, bent form looked likely to overwhelm her at any second. As I came hurrying up, I could hear him saying:

‘It's you they don't like in there, my dear. When I used to frequent this place by myself, they always treated me like royalty. Oh yes, like royalty. Don't like women of your sort. They only want real ladies or else whores. And you're neither. So you see, they don't like you one bit. Never had any trouble here until you insisted on tagging along.’

‘Come along, darling. Here's Christopher. Well done, Christopher. Look, darling, he's found Boris for us.’

It was not a great distance to the Metropole, but the car could often move at no more than a crawl through the pedestrians and rickshaws. Throughout the journey, Sarah continued to hold Sir Cecil by the arm and shoulder while he drifted in and out of sleep. Whenever he came round, he would try to shake Sarah off, but she would laugh and continue to hold him steady in the lurching vehicle.

It was my turn to assist him as we negotiated the revolving doors of the Metropole, and then the lift, while Sarah exchanged cheerful greetings with the lobby staff. Then we were finally up in the Medhursts’ suite and I was able to lower Sir Cecil into an armchair.

I thought he would doze off, but instead he grew suddenly alert again and began asking me some meaningless questions of which I could make neither head nor tail. Then when Sarah emerged from the bathroom with a flannel and began to mop his forehead, he said to me:

‘Banks, my boy, you can speak frankly. This wench here. As you see, she's a good few years younger than me. No spring chicken herself, mind you, ha ha! But still, a good few years my junior. Tell me frankly, my boy, do you suppose, in a place like tonight's, where you found us tonight, a place like that, do you suppose a stranger looking at the two of us together … Well, let's speak frankly! What I'm asking you is, do you suppose people take my wife for a harlot?’

Sarah's expression, as far as I could see it, did not change, though a slight urgency entered her ministrations, as though she hoped the treatment would bring a change of mood. Sir Cecil waved his head in irritation as though avoiding a fly, then said:

‘Come on, my boy. Do speak frankly now.’

‘Now, now, darling,’ Sarah said quietly. ‘You're being unpleasant.’

‘I'll tell you a secret, my boy. I'll tell you a secret. I rather enjoy it. I like people to mistake my wife for a harlot. That's why I like to frequent places like that one tonight. Get off me! Leave me alone!’ He pushed Sarah aside, then continued: ‘Other reason I go, of course, no doubt you guessed it, I owe a little money. Run up bit of a debt, you know. Nothing I won't win back, of course.’

‘Darling, Christopher's been very kind. You mustn't bore him.’

‘What's the harlot saying? Hear what she said, my boy? Well, don't. Don't listen to her. Don't listen to trollops, that's what I say. They'll lead you astray. Particularly in times of war and conflict. Never listen to a trollop in times of war.’

He climbed to his feet unaided, and for a moment stood swaying before us in the middle of the room, his unfastened collar sticking out from his neck. Then he moved off into the bedroom, closing the door behind him.

Sarah gave me a smile, then went in after him. Had it not been for that smile – or rather, something like an appeal I detected behind it – I would certainly have withdrawn at that point. As it was, I remained in the room, examining absent-mindedly a Chinese bowl on a stand near the entrance. For a time, I could hear Sir Cecil shouting something; then there was silence.

Sarah emerged after perhaps five minutes and looked surprised to find me still there.

‘Is he all right?’ I asked.

‘He's asleep now. He'll be fine. I'm sorry you were inconvenienced, Christopher. Hardly what you were seeking when you came looking for us this evening. We'll arrange something to make up. We'll take you out to dinner somewhere. Astor House has good food still.’

She was guiding me out of the room, but I turned at the door and said:

‘This sort of thing. Does it happen a lot?’

She gave a sigh. ‘Often enough. But you mustn't think I mind. It's just that I do worry sometimes. About his heart, you know. That's why I always go with him now.’

‘You look after him well.’

‘You mustn't get the wrong impression. Cecil's a dear man. We must take you out to dinner very soon. When you're not busy. But I suppose you're always busy.’

‘Is this how Sir Cecil tends to pass all his evenings?’

‘Most of them. Some of his days too.’

‘Is there anything at all I can do?’

‘Anything you can do?’ She gave a light laugh. ‘Look, Christopher, I'm fine. Really, you mustn't get the wrong impression about Cecil. He's a dear. I … I do love him so.’

‘Well, then, I'll say goodnight.’

She took another step towards me and raised a hand vaguely. I found myself grasping it, but not quite knowing what to do next, kissed the back of it. Then, mumbling another goodnight, I stepped into the corridor.

‘You're not to worry about me, Christopher,’ she whispered from the door. ‘I'm perfectly all right.’

Those were her words to me last night. But today, it is those earlier words of hers, uttered three weeks ago when I first saw her at the ballroom of the Palace Hotel, that return to me with particular pertinence. ‘I don't expect we'll be going anywhere in a hurry,’ she had said. ‘Unless someone comes to the rescue.’ What could she have intended by making such a remark to me that evening? As I say, even at the time it puzzled me, and I may well have quizzed her further about it had not Grayson, just at that moment, emerged out of the crowd, looking for me.