There was nothing. The street which contained the restaurant was dark but entirely empty. At the end a broader street crossed over it, and this was lit by the faint flicker of torch flame, but that, too was deserted.

'Cort? What is it?' I asked.

'It's him. He's there again.'

I looked at him blankly, but Cort did not respond. He continued staring, as though frightened out of his wits.

I touched him gently on the arm to stir him; he did not react immediately, but eventually his eyes moved away from the blank point they were staring at, and he looked at me. He seemed dazed and confused.

'Whatever is the matter?' I asked, feeling a quite genuine concern as much as a very real curiosity. My mind went back to what Longman had said about Cort having a breakdown from the strain of his task at the palazzo. Was this a manifestation of his troubles? I had little enough experience of such things.

'I do beg your pardon,' he said eventually in a faltering voice. 'Quite absurd of me. Please forget it. I must go now.'

'Certainly not,' I replied. 'I have no idea what is distressing you, but I could not possibly leave you alone just yet. Come! I will walk with you. It is no trouble, and I feel like a stroll in any case. If you do not wish to talk, we will pace the streets together in solemn silence and enjoy the night air. Have no fear that I wish to pry into your affairs. Although I do, of course.'

He smiled at that, and allowed me to lead him towards the alley's end. Then he pointed to the left, away from San Marco, and indicated that we should head in that direction. He said nothing for a long while. We had passed the Rialto before he groaned loudly and scratched his head furiously with both hands. 'You must forgive that performance,' he said with an effort to return to normal. 'I must have seemed absurd.'

'Not at all,' I replied in what I hoped was a reassuring manner, 'but you did alarm me. Do you wish to tell me what it was that so distressed you?'

'I would, were I not afraid that Longman would hear of it. He is a terrible gossip, and I do not wish to become an object of ridicule.'

'Have no fear of that,' I replied. 'I would not tell Mr Longman anything of importance. Should you come to know me better you will realise that any confidence consigned to my care is perfectly safe.'

Which was true. A natural tendency on my part had been confirmed by my experiences in the City, where knowledge is all. Exclusive possession of a fact is worth far more than money. Money you can borrow; knowledge has a higher price. Say (for example) that you hear a company has struck gold in South Africa. It is easy enough to borrow some money to buy shares in it before they rise, and make a profit. All the money in the world will not help you if you do not discover this fact before everyone else. I have never in my life traded without advance knowledge, and I do not know of anyone with sense who has done so either.

'Well, then. I would like to relate my experiences, if you are prepared to listen, and also promise to stop me should you find my story ridiculous or dull.'

'I promise.'

He took a deep breath and began.

'I mentioned that I was sent here by my uncle, to fulfil a contract with the Albemarle family. I arrived some five months ago with my family, and took up operations as best I could. It has not been easy, and would have strained even a native speaker with more experience than I possess. The house is in far worse shape than I was led to believe, the workforce is erratic, and finding the right materials difficult and expensive. My wife did not want to come, and is deeply unhappy, poor woman.

'You might not believe it from what you have seen, but I have made progress, although every advance is matched by some setback. Everything is way behind schedule and far above the budget, of course, but that is because the family had no conception whatsoever of the task they had taken on.

'That is not what is giving me such concern, although I am quite prepared to countenance the idea that the strain makes me more susceptible. I have always been of a nervous disposition. I do not imagine for a moment that someone like you – who seem very sound and sensible – let alone a man like Macintyre, would be subject to the torments I have endured in the past few weeks.

'In brief, I have become the victim of hallucinations of the most terrible kind. Except that I cannot fully accept that this is what they are. They are too real to be fictitious, yet too bizarre to be real.

'I should tell you that I am an orphan; my mother died giving birth to me, and my father shortly thereafter. That is why I was brought up by my mother's sister, and her husband, the architect. My mother died in Venice. They had been travelling Europe on an extended honeymoon and stopped here for a few months while they prepared for my birth.

'I lived; she died. There is nothing else to add, except to say that my father was heartbroken. I was sent back to England to my aunt and he continued his travels to recover. Alas, he caught a fever in Paris while on the verge of returning to England, and died as well. I was two years old at the time. I remember nothing of either of them, and know only what I have been told.

'Please do not think I am talking off the point when I mention this. I was perfectly healthy in mind and body until I came here. I was brought up properly and well; I am not certain I was suited by nature to be an architect, but I may in time turn out to be perfectly competent. There is nothing in my past at all to foreshadow what has been happening to me here, the place of my mother's death.

'It all began when I was walking along a street, going to a mason's yard, as I recall, and I saw an old man walking towards me. There was nothing about him to excite any interest, and yet I found myself looking at him in the way you do when you see something that fascinates, yet know you should not look. You look away and find your eyes straying back again, and again.

'As he drew near he bowed, and then we passed, each going on his separate way. I turned round to look at him again, and he was gone.'

'That was it?' I asked in some surprise, as he seemed to think that nothing more needed to be said.

'The first time, yes. As your tone suggests, there was nothing to cause any concern; indeed, it was not even clear why I should have noticed him. Nonetheless, it disturbed me, and I found my mind going back to the moment. Then it happened again.

'I was walking along the Riva this time. It was mid-afternoon, and the loafers and wastrels were all there, sitting on the ground, cluttering up the steps of the bridges, idling away the hours as is the custom. I was in a hurry; I had an appointment and I was late. I was walking up the steps of a bridge and looked up, and there he was again. I slowed down, just a little, when I saw him, and he reached inside his coat, pulled out a watch and looked at it. Then he smiled at me as if to say, you're late.

'I hurried past, feeling almost stung by the implied reproach and determinedly kept on my way. This time I didn't look back. He knew I was late, you see. He knows about me. He must be watching me, finding out about me.'

'But you know nothing about him?'

'No.'

'And this person you were going to visit. He couldn't have said something? Did you ask?'

'Impossible,' he said shortly.

'Describe this man to me.'

We were walking slowly, and as far as I was concerned, aimlessly. I assumed that Cort knew where he was going. Certainly he turned left and right as though he was following some course, rather than wandering lost in thought as he talked. Walking the silent, deserted streets, our footfalls echoing between the buildings, accompanied by the lap of water and the occasional reflection of moonlight in the canals when the clouds cleared, created a strange and wonderful atmosphere that Cort's tale enhanced rather than dissipated.