The police station looked to be abandoned. As I came down the slope, I could see broken windows and one of the entrance doors hanging off its hinges. But when I picked my way through the broken glass and went inside into the station's reception area, I was met by three Chinese men, two of whom pointed rifles at me, while the third brandished a garden spade. One of them – who was wearing a Chinese Army uniform – asked in halting English what I wanted. When I managed to convey who I was, and that I wished to speak with whomever was in charge, the men began to argue among themselves. Eventually the one holding the spade disappeared through into a back room, and the others kept their guns on me while we waited for his return. I took the opportunity to glance about me, and concluded it was unlikely there were any policemen left in the station. Although a few posters and notices remained up, the place looked to have been abandoned some time ago. Cables were dangling off one wall and the back section of the room had been gutted by fire.

After perhaps five minutes, the man with the spade came back. A few more exchanges followed in what I guessed was Shanghai dialect, before finally the soldier gestured that I should go with the man with the spade.

I followed the latter through into a back room, which turned out also to be guarded by armed men. But these stood aside for us, and soon I was going down some rickety stairs into the cellars of the police station.

My recollection is a little hazy now as to how we got down to the bunker. There were perhaps a few more rooms; I remember we walked along a kind of tunnel, stooping to avoid low beams; here too were sentries, and each time we encountered one of their looming black shapes, I was obliged to press myself right into the rough wall in order to squeeze past.

Eventually I was shown inside a windowless room that had been turned into some sort of makeshift military headquarters. It was lit by two bulbs dangling side by side from a central beam. The walls were of exposed brick, and in the wall to my right, there was gouged out a hole large enough for a man to climb through. There was a battered wireless set mounted in the opposite corner, while in the middle of the floor sat a big office desk – which I could see at a glance had been sawn in half, then crudely put back together again with rope and nails. Several upturned wooden boxes constituted the available seating, the only actual chair being occupied by an unconscious man who was tied up to it. He was in a Japanese marines’ uniform, and one side of his face was a mass of bruising.

The only other people present were two Chinese Army officers, both on their feet, bent over some chart spread across the desk. They looked up as I entered, then one of them came forward and offered his hand.

‘I am Lieutenant Chow. This is Captain Ma. We are both very honoured to have you visit us like this, Mr Banks. Have you come to lend us your moral support?’

‘Well, in actual fact, Lieutenant, I came here with a specific request. However, I would hope that once my task is completed, morale will be boosted no end. Yours and everyone else's. But I'll need a little assistance, and this is why I've come to you.’

The lieutenant said something to the captain, who evidently did not understand English; then they both looked at me. Suddenly the unconscious Japanese in the chair vomited down the front of his uniform. We all turned to stare at him; then the lieutenant said:

‘You say you need assistance, Mr Banks. In what form exactly?’

‘I have here some directions, directions to a particular house. It's imperative I reach this house without any further delay.

The directions are written in Chinese, which I'm unable to read. But you see, even if I could read them, I'd need a guide, someone familiar with this locality.’

‘So you wish for a guide.’

‘Not only that, Lieutenant. I will need four or five good men, more if possible. They will need to be trained and experienced, since this will be a delicate task.’

The lieutenant gave a little laugh; then making his features solemn once more, said: ‘Sir, we are at this moment very short of such men. This base is a crucial part of our defence force. And yet you saw for yourself how thinly it is guarded. In fact, the men you saw on the way in are either wounded, sick or inexperienced volunteers. Every man capable of sustained fighting we have pushed to the front.’

‘I appreciate, Lieutenant, that you're in a demanding situation. But you have to understand, I'm not talking about just some casual enquiry I wish to make. When I say it's imperative I reach this house … Well, Lieutenant, I'll tell you, there's no need to keep it a secret. You and Captain Ma here can be the first to know. The house I wish to find, which I know is very near us now, is none other than the one in which my parents are being held. That's right, Lieutenant! I'm talking about nothing less than the solving of this case after all these years. You see now why I felt my request, even at this busy moment for you, quite warranted.’

The lieutenant's face remained fixed on mine. The captain asked him something in Mandarin, but the lieutenant did not reply. Then he said to me:

‘We are waiting for some men to return from a mission. Seven went out. We do not know if they will all return. It was my intention that they be sent to another location immediately. But now … In this instance, I shall take personal responsibility. These men, however many of them may return, will accompany you on your mission.’

I sighed impatiently. ‘I thank you, Lieutenant. But how long will we have to wait for these men? Isn't it possible for me to take a few of the men standing out there, just for several minutes? After all, the house is somewhere very near here. And you see, I have someone waiting …’ I suddenly remembered Sarah, and a kind of panic seized me. I took another step forward and said: ‘In fact, Lieutenant, I wonder if I may use your telephone. I really should speak to her.’

‘I'm afraid there is no telephone here, Mr Banks. That is a radio, connected only with our headquarters and our other bases.’

‘Well then, it's all the more imperative I clear this matter up without delay! You see, sir, there is a lady waiting, even as we speak! May I suggest I take three or four of the men out there guarding this base …’

‘Mr Banks, please calm yourself. We will do all we can to assist you. But as I have said already, the men outside are not fit for such a mission. They will only jeopardise it. I understand you have waited many years to solve this case. I would counsel you not to act hastily at this juncture.’

There was good sense in the lieutenant's words. With a sigh, I sat down on one of the upturned tea-chests.

‘The men should not be much longer now.’ said the lieutenant. ‘Mr Banks, may I see these directions you have?’

I was reluctant to let go of my notebook even for a few seconds. But in the end I handed it to the officer, opened at the appropriate pages. He studied the directions for a while, then returned the notebook to me.

‘Mr Banks, I should tell you. This house. It will not be so easy to reach.’

‘But I happen to know, sir, it's very near here.’

‘It is near, that is true. Nevertheless, it will not be easy. Indeed, Mr Banks, it may even be behind Japanese lines by now.’

‘Japanese lines? Well, I suppose I could always reason with the Japanese. I have no quarrel with them myself.’

‘Sir, if you will come with me. I will show you, while we wait for the men, our exact position.’

For a moment, he spoke rapidly to the captain. He then walked towards a broom cupboard in the corner, flung open its door and stepped inside. It took me a moment to realise I was expected to follow, but then when I tried also to enter the cupboard, I almost walked into the heels of the lieutenant's boots – which were now directly in front of my face. I heard his voice say from the darkness above:

‘If you will please follow me, Mr Banks. There are forty-eight rungs. It is better you keep at least five rungs below me.’

His feet disappeared. Stepping further into the cupboard, I reached out my hands and found some metal rungs on the brick before me. Far above in the darkness, I could see a little pond of sky. I guessed that we were at the bottom of a chimney, or an observation tower used by the police.

For the first few rungs, I found the going awkward; not only was I nervous of missing my grip in the dark, there was also the worry of the lieutenant slipping and falling down on to me. But eventually the patch of sky grew larger, and then I saw the lieutenant's figure clambering out above me. In another minute or so, I had joined him.

We were standing up on a high flat roof surrounded on all sides by miles of densely packed rooftops. Away in the distance, perhaps a half-mile to the east, I could see a column of dark smoke rising into the late-afternoon sky.

‘It's odd,’ I said, looking around me. ‘How do people get about down there? There appear to be no streets.’

‘That is certainly how it looks from up here. But perhaps you will care to look through these.’

He was holding out a pair of binoculars. I raised them to my eyes and spent some time adjusting them until I could see clearly, only to find I was gazing at a chimney stack a few yards in front of me. Eventually, though, I managed to focus on the column of smoke in the distance. The lieutenant's voice said somewhere close beside me:

‘You are now looking at the warren, Mr Banks. The factory workers live there. I am sure in all the time you were a child here, you never visited the warren.’

‘The warren? No, I don't think so.’

‘Almost certainly not. Foreigners rarely see such places unless they are missionaries. Or perhaps communists. I am Chinese, but I too, like many of my peers, was never permitted to go near such places. I knew almost nothing about the warren until ’32, the last time we fought the Japanese. You would not believe human beings could live like that. It is like an ants’ nest. Those houses, they were intended for the poorest people. Houses with tiny rooms, row after row, back to back. A warren. If you look carefully, you may see the lanes. Little alleys just wide enough to allow the people to get into their homes. At the back, the houses have no windows at all. The rear rooms are black holes, backing on to the houses behind. Forgive me, I am telling you this for a good reason, as you will see. The rooms were made small, because they were for the poor. There was a time when seven or eight people shared such a room. Then as the years went on, families were forced to make partitions, even within these small rooms, to share the rent with another family. And if they still couldn't pay the landlords, they would partition the room further. I remember seeing tiny black closets divided four times, each with a family in it. You do not believe this, Mr Banks, that human beings can live like this?’

‘It does seem unbelievable, but if you've seen these conditions yourself, Lieutenant …’

‘When the fight against the Japanese is over, Mr Banks, I will consider giving my services to the communists. You think that is a dangerous thing to say? There are many officers who would rather fight under the communists than under Chiang.’

I moved the binoculars over the dense mass of shabby roofs. I could see now that many of them were broken through. I could decipher, moreover, the lanes the lieutenant had mentioned, narrow passageways threading here and there into the tenements.

‘But this is no shanty town,’ the lieutenant's voice was continuing. ‘Even if the partitions erected by the tenants are flimsy, the essential structure, the warren itself, is brick. This proved crucial in ’32 when the Japanese attacked, and it is proving so to us now.’

‘I can see that,’ I said. ‘A solid warren defended by soldiers. No easy prospect for the Japanese, even with their modern weapons.’

‘You are right. The Japanese weaponry, even their training, counts for almost nothing down there. Fighting is reduced to rifles, bayonets, knives, pistols, spades, meat cleavers. The Japanese line, in the past week, has actually been pushed back. You see that smoke, Mr Banks? That point was held by the enemy only last week. But now we have pushed them back.’

‘Are there civilians still living down there?’

‘There are indeed. You may not believe it, but even close to the front, some of the houses in the warren are still occupied. This makes it even harder for the Japanese. They cannot shell indiscriminately. They know the Western powers are watching and they fear ruthlessness will have a cost.’

‘How long can your troops hold out?’

‘Who knows? Chiang Kai-shek may send us reinforcements. Or the Japanese might decide to give up and redeploy, concentrate instead on Nanking or Chunking. It is by no means certain we will not still be victorious. But the fighting recently has cost us dearly. If you will move your field glasses to the left, Mr Banks. Now, do you see that road? Yes? That road is known locally as Pigs’ Alley. It doesn't look an impressive road, but now it is very important to the outcome. As you see, that is the one road that runs along the edge of the warren. At the moment, our troops have sealed it off, and have managed to keep the Japanese out. If they are able to come down that road, the warren can be penetrated all along the side. There will be no point in our attempting to hold out. We will have been flanked. You asked for men to accompany you to the house where your parents are. The men who will accompany you would otherwise have been deployed defending the barricade at the top of Pigs’ Alley. The last few days, the fighting there has become desperate. Meanwhile, of course, we are having also to hold our line across the warren.’

‘From up here, you wouldn't think there was so much going on down there.’

‘Indeed. But I can assure you, inside the warren, things are now very bad. I tell you this, Mr Banks, since you are intending to go in there.’

For a moment or two, I went on gazing through the glasses in silence. Then I said: ‘Lieutenant, that house, the house where my parents are being held. Will I be able to see it from up here?’

His hand touched my shoulder briefly, though I did not take my eyes from the binoculars.

‘Do you see, Mr Banks, the remains of that tower standing to the left? It looks like one of those Easter Island figures. Yes, yes, that's it. If you draw a line from that over to the remains of that large black building to the right, the old textile warehouse, that was, this morning, the line to which our men had beaten back the Japanese. The house where your parents are being held is roughly level with that tall chimney on your left. If you draw a line, very level with it across the warren, until you come to just a little left of where we are now standing. Yes, yes …’

‘You mean near that roof, the one with the eaves pointing up into a kind of arch …’

‘Yes, that's it. Of course, I cannot say with certainty. But according to those directions you showed me, that is roughly where the house is.’

I stared through the field glasses at that particular roof. For some time I could not stop staring, even though I was conscious of keeping the lieutenant from his duties. After a while, it was the lieutenant who said:

‘It must feel strange. To think you might be looking at the very house containing your parents.’

‘Yes. Yes, it does feel a little strange.’

‘Of course, it might not be that house. That was simply a guess on my part. But it will be somewhere very near it. That tall chimney I showed you, Mr Banks. The locals refer to it as the East Furnace. The chimney you can see much closer to us, almost directly in line with the other one, belongs to the West Furnace. Before the fighting, the inhabitants used to burn their refuse at one or other of these places. I would advise you, sir, to use the furnaces as your landmarks once you are within the warren. Otherwise it is hard for a stranger to keep his bearings. Look again carefully at that far chimney, sir. Remember, the house you seek is only a little way away from it, in a direct line due south.’

I finally lowered the binoculars. ‘Lieutenant, you've been most kind. I can't tell you how grateful I am to you. In fact, if it won't embarrass you, you will perhaps permit me to mention you by name during the ceremony that will take place at Jessfield Park to commemorate the freeing of my parents.’

‘Really, my help has not been so significant. Besides, Mr Banks, you must not assume your task is accomplished. Standing up here, it does not look far away. But inside the warren there is a lot of fighting. Although you are not a combatant, it will still be difficult to move from house to house. And aside from the two furnaces, there are few clear landmarks surviving. Then you must bring your parents out safely. In other words, you still have a daunting task ahead of you. But now, Mr Banks, I suggest we go back down. The men may well have returned by now and be awaiting my orders. And as for you, Mr Banks, you must try and come back before nightfall. It is hellish enough moving about the warren in daylight. At night, it will be like drifting through one's worst nightmares. If you are overtaken by darkness, I would advise you to find some safe place and wait with the men until morning. Only yesterday, two of my men killed each other, they were so disorientated in the dark.’

‘I've taken to heart everything you've said, Lieutenant. Well then, let's be going back down.’

Downstairs, Captain Ma was talking to a soldier in a badly torn uniform. The latter did not appear to be wounded, but seemed shocked and upset. The Japanese in the chair was now snoring, as though enjoying a peaceful nap, though I noticed he had vomited some more down the front of his clothes.

The lieutenant conferred quickly with the captain, then questioned the soldier in the torn uniform. Then he turned to me and said:

‘It is bad news. The others have not returned. Two have certainly been killed. The remainder are trapped, although there is a good chance they will yet escape. The enemy has, if only temporarily, made an advance, and it may well be that the house your parents are in is now behind their lines.’

‘Regardless of that, Lieutenant, I still need to proceed, and without any further delay. Look here, if the men you promised me haven't returned, then perhaps, though I realise it's a lot to ask, perhaps you'd be good enough to escort me yourself. Honestly, sir, I can't think of a more suitable person to assist me at this point.’

The lieutenant thought this over with a grave expression. ‘Very well, Mr Banks,’ he said finally. ‘I shall do as you ask. But we must hurry. I should not really leave this post at all. To do so for any length of time could have the most awful consequences.’

He issued rapid instructions to the captain, then opening a drawer in the desk, began placing a number of items into his pockets and belt.

‘It is better you do not carry a rifle, Mr Banks. But do you have a pistol? No? Then take this. It is German and very reliable. You should keep it concealed and if we encounter the enemy, you must not hesitate to declare your neutrality immediately and clearly. Now, if you will follow me.’

Taking a rifle that was leaning against the desk, he strode over to the hole gouged into the opposite wall and nimbly climbed through. I pushed the pistol into my belt, where it was more or less concealed by my jacket, then hurried after him.