‘But you were too late. Bad luck. Still, it was hardly your fault – your client cannot reasonably blame you for witnessing a road accident.’

He looked increasingly uncomfortable and was sweating even more. I made to move away but he grabbed me and held me by the arm so fiercely that it was painful.

‘The last picture,’ he said, his breath foetid in my face, ‘the Venetian scene. You obtained it and I must have it. I will pay you what you ask, with a good profit, you will not lose. It is in your interests after all, you would only sell it on later. What is your price?’

I wrenched my arm from his grip. ‘There is none. The picture is not for sale.’

‘Don’t be absurd man, my client is wealthy, you can name your price. Don’t you understand me – I have to have that picture.’

I had heard enough. Without troubling about good manners, I turned on my heel and walked away from him.

But he was there again, pawing at me, keeping close to my side. ‘You have to sell the picture to me.’

‘If you do not take your hands off I will be obliged to call the porters.’

‘My client gave me instructions ... I was not to go back without the picture. It has taken years to track it down. I have to have it.’

We had reached the cashier’s office, where there was now, of course, a considerable queue of buyers waiting to pay. ‘For the last time,’ I hissed at him, ‘let me alone. I have told you. I want the picture. I bought it and I intend to keep it.’

He took a step back and, for a moment, I thought that was that, but then he leaned close to me and said, ‘You will regret it. I have to warn you. You will not want to keep that picture.’

His eyes bulged, and the sweat was running down his face now. ‘Do you understand? Sell me the picture. It is for your own good.’

It was all I could do not to laugh in his face but, instead, I merely shook my head and turned away from him, to stare at the grey cloth of the jacket belonging to the man in front of me as if it were the most fascinating thing in the world.

I dared not look round again but by the time I had left the cashier’s window having paid for my purchases, including the Venetian picture, the man was nowhere to be seen.

I was relieved and dismissed the incident from my mind as I went out into the sunshine of St James’s.

It was only later that evening, as I was settling down to work at my desk, that I felt a sudden, strange frisson, a chill down my spine. I had not been in the least troubled by the man – he had clearly been trying to make up some tale about the picture to convince me I should let him have it. Nevertheless, I felt uneasy.

Everything I had bought at the auction was delivered the next day and the first thing I did was take the Venetian picture across London to a firm of restorers. They would clean it expertly, and either repair the old frame or find another. I also took one of the others to have a small chip made good and because picture restorers work slowly, as they should, I did not see the paintings again for some weeks, by which time I had returned here to the Cambridge summer term that was in full swing.

I brought all the new pictures with me. I was in my London rooms too infrequently to leave anything of much value or interest there. I placed the rest with ease but wherever I put the Venetian picture it looked wrong. I have never had such trouble hanging a painting. And about one thing I was adamant. I did not want it in the room where I slept. I did not even take it into the bedroom. Yet I am not a superstitious man, and up until that time had only ever suffered nightmares if I was ill and had a fever. Because I had such trouble finding the right place for it, in the end I left the painting propped up there, against the bookcase. And I could not stop looking at it. Every time I came back into these rooms, it drew me. I spent more time looking at it – no, into it – than I did with pictures of far greater beauty and merit. I seemed to need it, to spend far too much time looking into every corner, every single face.

I did not hear any more from the tiresome pest in the auction rooms, and I soon forgot about him entirely.

Just one curious thing happened around that time. It was in the autumn of the same year, the first week of Michaelmas term and a night when the first chills of autumn had me ring for a fire. It was blazing up well, and I was working at my desk, in the circle of lamplight, when I happened to glance up for a second. The Venetian painting was directly in my sight and something about it made me look more closely. Cleaning had revealed fresh depths to the picture, and much more detail was now clear. I could see far more people who were crowded on the path beside the water, several rows deep in places, and gondolas and other craft laden with revellers, some masked, others not, on the canal. I had studied the faces over and over again, and each time I found more. People hung out of windows and over balconies, more were in the dim recesses of rooms in the palazzi. But now, it was only one person, one figure, which caught my eye and stood out from all the rest, and although he was near the front of the picture, I did not think I had noticed the man before. He was not looking at the lagoon or the boats, but rather away from them and out of the scene – he seemed, in fact, to be looking at me, and into this room. He wore clothes of the day but plain ones, not the elaborate fancy dress of many of the carnival-goers, and he was not masked. But two of the revellers close to him wore masks and both appeared to have their hands upon him, one on his shoulder, the other round his left wrist, almost as if they were trying to keep a hold of him or even pull him back. His face had a strange expression, as if he were at once astonished and afraid. He was looking away from the scene because he did not want to be part of it and into my room, at me – at anyone in front of the picture – with what I can only describe as pleading. But for what? What was he asking? The shock was seeing a man’s figure there at all when I had previously not noticed it. I supposed that the lamplight, cast on the painting at a particular angle, had revealed the figure clearly for the first time. Whatever the reason, his expression distressed me and I could not work with my former deep concentration. In the night, I woke several times, and, once, out of a strange dream in which the man in the picture was drowning in the canal and stretching out his arms for me to save him, and so vivid was the dream that I got out of bed and came in here, switched on the lamp and looked at the picture. Of course nothing had changed. The man was not drowning though he still looked at me, still pleaded, and I felt that he had been depicted trying to get away from the two men who had their hands on him.

I went back to bed.

And that, for a very long time, was that. Nothing more happened. The picture stayed propped up on the bookcase for months until eventually I found a space for it there, where you see it now.

I did not dream about it again. But it never lessened its hold on me, its presence was never anything but powerful, as if the ghosts of all those people in that weirdly lit, artificial scene were present with me, forever in the room.

Some years passed. The painting did not lose any of its strange force but of course everyday life goes on and I became used to it. I often spent time looking at it though, staring at the faces, the shadows, the buildings, the dark rippling waters of the Grand Canal, and I also vowed that one day I would go to Venice. I have never been a great traveller, as you know; I love the English countryside too much and never wanted to venture far from it during vacations. Besides, in those days I was busy teaching here, performing more and more duties within the college, researching and publishing a number of books and continuing to buy and sell some pictures, though my time for that was limited.