Dyson? if you want to know my theory, it is this: I believe that Dr. Black killed his wife.’

“ ‘But the verdict,’ I answered, ‘the verdict was given from your own evidence.’

“ ‘Quite so; the verdict was given in accordance with the evidence of my colleague and myself, and, under the circumstances, I think the jury acted very sensibly. In fact, I don’t see what else they could have done. But I stick to my opinion, mind you, and I say this also. I don’t wonder at Black’s doing what I firmly believe he did. I think he was justified.’

“ ‘Justified! How could that be?’ I asked. I was astonished, as you may imagine, at the answer I had got. The doctor wheeled round his chair and looked steadily at me for a moment before he answered.

“ ‘I suppose you are not a man of science yourself? No; then it would be of no use my going into detail. I have always been firmly opposed myself to any partnership between physiology and psychology. I believe that both are bound to suffer. No one recognises more decidedly than I do the impassable gulf, the fathomless abyss that separates the world of consciousness from the sphere of matter. We know that every change of consciousness is accompanied by a rearrangement of the molecules in the grey matter; and that is all. What the link between them is, or why they occur together, we do not know, and most authorities believe that we never can know. Yet, I will tell you that as I did my work, the knife in my hand, I felt convinced, in spite of all theories, that what lay before me was not the brain of a dead woman—not the brain of a human being at all. Of course I saw the face; but it was quite placid, devoid of all expression. It must have been a beautiful face, no doubt, but I can honestly say that I would not have looked in that face when there was life behind it for a thousand guineas, no, nor for twice that sum.’

“ ‘My dear sir,’ I said, ‘you surprise me extremely. You say that it was not the brain of a human being. What was it, then?’

“ ‘The brain of a devil.’ He spoke quite coolly, and never moved a muscle. ‘The brain of a devil,’ he repeated, ‘and I have no doubt that Black found some way of putting an end to it. I don’t blame him if he did. Whatever Mrs. Black was, she was not fit to stay in this world. Will you have anything more? No? Good-night, good-night.’

“It was a queer sort of opinion to get from a man of science, wasn’t it? When he was saying that he would not have looked on that face when alive for a thousand guineas, or two thousand guineas, I was thinking of the face I had seen, but I said nothing. I went again to Harlesden, and passed from one shop to another, making small purchases, and trying to find out whether there was anything about the Blacks which was not already common property, but there was very little to hear. One of the tradesmen to whom I spoke said he had known the dead woman well; she used to buy of him such quantities of grocery as were required for their small household, for they never kept a servant, but had a charwoman in occasionally, and she had not seen Mrs. Black for months before she died. According to this man Mrs. Black was ‘a nice lady,’ always kind and considerate, and so fond of her husband and he of her, as every one thought. And yet, to put the doctor’s opinion on one side, I knew what I had seen. And then after thinking it all over, and putting one thing with another, it seemed to me that the only person likely to give me much assistance would be Black himself, and I made up my mind to find him.