Doctor Marrande, one of the most eminent psychiatrists in the country, had invited three of his colleagues and four others in the field of the natural sciences to spend an hour at his clinic considering the case of one of his patients. When they were all gathered, he said to them: ‘I should like to present to you the strangest and most disturbing case I have ever come across. I shall say nothing ahead of time about this patient, but let him speak for himself.’

The doctor rang and a man entered, accompanied by a member of staff. He was extremely thin, cadaverous even, as some madmen look when they are consumed by an obsession. Their bodies seem ravaged by one sick thought which devours them faster than any disease or consumption. Having greeted the company and sat down, the man spoke.

‘Gentlemen, I am well aware of what brings you here. I am happy to comply with Dr Marrande’s request for me to give you my history. For a long time he himself believed I was mad. Today he is not so sure. Some time in the near future you will realize that, unfortunately, not only for myself but for you and all the rest of humanity, my mind is as healthy, clear and as lucid as your own. Let me first of all give you the facts.

I am forty-two years old and unmarried. My income is sufficient for me to live a fairly luxurious kind of life. I live in a property which I own on the banks of the Seine at Biessard, near Rouen. I like hunting and I like fishing. Beyond the rocky hillsides behind my house lies one of the most beautiful forests in the whole of France, the forest of Roumare. And in front of the house, which is very large and very old, lies one of the most beautiful rivers in the world. Moreover, the house itself is attractive: it is painted white and stands in the middle of parkland which extends as far as the rocky hillsides I mentioned earlier.

My staff consists, or rather consisted, of a coachman, a gardener, a manservant, a cook and a laundry-cum-scullery maid. All these people had lived there with me for between ten and sixteen years. They were long familiar with my ways, with the running of the house, with the neighbourhood, everything. They made an excellent, harmonious team, a point which it is important to bear in mind in what follows.

I should add that since the Seine, as you probably know, is navigable as far as Rouen, on the stretch of it in front of my house I used to see daily all kinds of sea-going vessels from all over the world pass up and down stream, some under sail, some under steam.