'Of course. That is a matter of war.'

'No,' he replied, wagging a finger in correction. 'No war has been declared. We would be committing an outright theft from a nation which has done us no harm, and whose Government is currently almost cordial towards us, despite popular opinion.'

'Which cordiality may turn out to be a mere deception. It is obviously legitimate to discover if someone wishes you harm. Naturally it would be permissible to steal this information.'

'And if someone tries to prevent this theft? A guard or soldier? Even a member of the public? What measures could be taken against them?'

'Any that were required.'

'Including killing them?'

'I very much hope that could be avoided. But if that was the only way of gaining information that might save thousands of lives, then yes.'

'I see. Let us reverse the question then. Suppose a Frenchman comes to this country to steal our plans for invading France. What measures could be taken against him, should his whereabouts and intentions become known?'

'We plan to invade France?' I asked, astonished. Again, he found my response amusing.

'We should,' he said with a chuckle. 'It is the army's job to prepare for all such possibilities. However, I very much doubt such a plan exists. Our generals have a long tradition of being woefully unprepared, and in any case they seem to find shooting people armed only with spears quite difficult enough. Nonetheless, such plans should exist, as it is obvious that sooner or later there will be another war in Europe, and we do not know if we will be able to stand by and watch. No matter. Assume, if you can, that the generals are better prepared and more far-seeing than they are. How to react to the presence of this Frenchman on our soil?'

'Stop him.'

'How?'

'By whatever means necessary.'

'But he is only trying to do that which you have already declared legitimate.'

'I act to save the lives of my countrymen. And would do so again in this case.'

'Lives of Englishmen are more valuable than lives of Frenchmen?'

'Not in the eyes of God, perhaps, but I have no responsibility for the well-being of the French, while I am bound to the inhabitants of my country.'

'So, that is two murders you have committed. Quite a bloodthirsty fellow, are you not, Mr Cort?'

'I am nothing of the sort,' I said. 'I specialise in the syndication of international loans.'

'So you do. So you do. And you travel widely in pursuit of your business. France, Germany, even Italy. I gather you are competent at the languages of those countries as well.'

'Yes.'

He smiled. 'I'd like you to do me a little favour,' he said, changing the subject abruptly. 'When you are in Paris next week, I'd be most grateful if you could pick up a package for me. And bring it back. Would you oblige me in that matter?'

'Plans to invade England?' I asked.

'Oh, goodness me, no! We have those already; they're really quite good. No, this is something quite different. This is of no great secrecy or importance, routine correspondence, that is all; I merely want to ensure it gets here swiftly. I planned to get someone else to do it, but, alas, he had a small accident and cannot assist me.'

'I'd be happy to assist,' I said. 'Except that I'm not going to Paris next week. I believe my employers have no plans at all to send me anywhere, at present.'

He smiled sweetly. 'So kind of you to come and meet me today,' he said. 'I have greatly enjoyed our little conversation.'

I hardly knew what to make of this strange encounter, and was eager to discuss it with my chief, Mr Hector Samson of Syndication. He, however, although normally very strict about time-keeping, never referred to my absence for so many hours and, when I raised the matter, changed the topic so swiftly I realised he did not even want to know. The only indication I had that my employers were aware of the meeting was a letter dropped on my desk late that afternoon. I was to go to Paris the following Monday to supervise the final details of the flotation of a loan for an American railway company, they of the unsustainable dividends, although naturally such misgivings were not to be communicated to the other participants. That was their problem; all Barings had to do was get rid of the stock as swiftly as possible. Anyway, it was a small matter, already settled, the centre of which was to be in London with only a small participation from one Paris bank. Barings' own correspondents in France could – and regularly did – supervise such matters, and Barings were notoriously tight-fisted about extravagances like sending people on journeys. Even I could reason out what had happened.

I filled up much of my time on my recent voyage from Calcutta reading some of those stories of espionage which are so popular these days, which amused me greatly. I sometimes wonder if those few people who suspect my activities believe that I live a life of equal excitement. I am glad to say I do not. All this running around over deserts and feats of daring against sinister foreigners and secret societies makes splendid entertainment, but I do not know anyone of sense who conducts business in such a way. All governments, naturally, can call on people who are more proficient with muscle than with brain in certain circumstances. That's what armies are for. The task of discovering a rival's intentions and capabilities is, by and large, conducted in a more civilised fashion. In general, it is as dangerous and exciting as a busy day on the Baltic Exchange.

Except, that is, for my first venture into the business, which very nearly resulted in my deciding to have nothing to do with Henry Wilkinson. Hang the Empire, was my opinion, if it depends on this sort of thing.

It happened like this: I took the train to Dover as my employers directed, crossed the Channel by steamer to Calais, and arrived at the Gare du Nord at seven in the evening. I then went to my hotel in the rue Notre-Dame des Victoires. Not a grand hotel by any means; the Baring family was far too cautious with its money to allow luxury; it was why many people hankered after a job with the Rothschilds, who had a finer appreciation of their employees' comforts. But it had running water, was clean and was only a short distance from the Bourse: I have stayed in much worse. My business, such as it was, could be dealt with in half an hour the following morning, and so I had the evening to myself. Or to attend to the note that was pushed under my door ten minutes after I arrived. It contained an address, and a time. Nothing more. 15, rue Poulletier. Nine o'clock.

Now, the hero of a spy story would have managed to discover the whereabouts of this address and get there with such ease it might not even be mentioned. I, on the other hand, took some forty-five minutes to acquire a map which even gave the location (shops never close in adventure stories; alas, they shut promptly at seven-thirty in reality) and then another hour to get there. Perhaps there was a tram which might have taken me, but I never discovered it. It was raining – a fine, persistent and depressing drizzle – and all the carriages were occupied. I had no umbrella, so had to walk, my hat getting sodden, my coat turning into blotting paper, into an area of Paris I had never even visited in daylight before.

This was the Ile Saint-Louis, an infested, rat-ridden tangle of criminality and sedition lying at the very heart of the city. It had once been fashionable and well-to-do, but those days had long since passed. Every building was crumbling and neglected, there was no street lighting (and, I guessed, not much progress had been made in installing modern sewage) and it was deathly quiet. The police of Paris never venture onto the island between sundown and sunrise; it becomes an independent country in the dark, answerable to no authority, and anyone who goes there must take full personal responsibility for his fate. Most of the revolutionaries, many of the anarchists and criminals who grace the pages of the popular press with their activities, give their address as the Ile Saint-Louis; they inhabit great houses which once echoed to the laughter of the aristocracy and now are cut up into dozens of squalid little rooms for rent by the month, the day or the hour. It is a den of cut-throats and fugitives, perfect for people who need or wish to disappear. The address I was seeking lay right at its heart, past the raddled women standing in the alleyways; past the men with narrow faces and suspicious eyes who watch as you walk by; past the long shadows, and sudden noises of something moving behind you; past the soft laughter that you hear faintly down side alleys.