About a month after the extraordinary and mysterious murder of Sir Thomas Vivian, the well-known and universally respected specialist in heart disease, Mr. Dyson called again on his friend Mr. Phillipps, whom he found, not as usual, sunk deep in painful study, but reclining in his easy-chair in an attitude of relaxation. He welcomed Dyson with cordiality.

‘I am very glad you have come,’ he began; ‘I was thinking of looking you up. There is no longer the shadow of a doubt about the matter.’

‘You mean the case of Sir Thomas Vivian?’

‘Oh, no, not at all. I was referring to the problem of the fish-hooks. Between ourselves, I was a little too confident when you were here last, but since then other facts have turned up; and only yesterday I had a letter from a distinguished F.R.S. which quite settles the affair. I have been thinking what I should tackle next; and I am inclined to believe that there is a good deal to be done in the way of so-called undecipherable inscriptions.’

‘Your line of study pleases me,’ said Dyson, ‘I think it may prove useful. But in the meantime, there was surely something extremely mysterious about the case of Sir Thomas Vivian.’

‘Hardly, I think. I allowed myself to be frightened that night; but there can be no doubt that the facts are patient of a comparatively commonplace explanation.’

‘Really! What is your theory then?’

‘Well, I imagine that Vivian must have been mixed up at some period of his life in an adventure of a not very creditable description, and that he was murdered out of revenge by some Italian whom he had wronged.’

‘Why Italian?’

‘Because of the hand, the sign of the mano in fica. That gesture is now only used by Italians. So you see that what appeared the most obscure feature in the case turns out to be illuminant.’

‘Yes, quite so. And the flint knife?’

‘That is very simple. The man found the thing in Italy, or possibly stole it from some museum. Follow the line of least resistance, my dear fellow, and you will see there is no need to bring up primitive man from his secular grave beneath the hills.’

‘There is some justice in what you say,’ said Dyson. ‘As I understand you, then, you think that your Italian, having murdered, Vivian, kindly chalked up that hand as a guide to Scotland Yard?’

‘Why not? Remember a murderer is always a madman. He may plot and contrive nine-tenths of his scheme with the acuteness and the grasp of a chess-player or a pure mathematician; but somewhere or other his wits leave him and he behaves like a fool. Then you must take into account the insane pride or vanity of the criminal; he likes to leave his mark, as it were, upon his handiwork.’

‘Yes, it is all very ingenious; but have you read the reports of the inquest?’

‘No, not a word. I simply gave my evidence, left the court, and dismissed the subject from my mind.’

‘Quite so. Then if you don’t object I should like to give you an account of the case. I have studied it rather deeply, and I confess it interests me extremely.’

‘Very good. But I warn you I have done with mystery. We are to deal with facts now.’

‘Yes, it is fact that I wish to put before you. And this is fact the first. When the police moved Sir Thomas Vivian’s body they found an open knife beneath him. It was an ugly-looking thing such as sailors carry, with a blade that the mere opening rendered rigid, and there the blade was all ready, bare and gleaming, but without a trace of blood on it, and the knife was found to be quite new; it had never been used. Now, at the first glance it looks as if your imaginary Italian were just the man to have such a tool. But consider a moment. Would he be likely to buy a new knife expressly to commit murder? And, secondly, if he had such a knife, why didn’t he use it, instead of that very odd flint instrument?

‘And I want to put this to you. You think the murderer chalked up the hand after the murder as a sort of “melodramatic Italian assassin his mark” touch. Passing over the question as to whether the real criminal ever does such a thing, I would point out that, on the medical evidence, Sir Thomas Vivian hadn’t been dead for more than an hour; That would place the stroke at about a quarter to ten, and you know it was perfectly dark when we went out at 9.30. And that passage was singularly gloomy and ill-lighted, and the hand was drawn roughly, it is true, but correctly and without the bungling of strokes and the bad shots that are inevitable when one tries to draw in the dark or with shut eyes. Just try to draw such a simple figure as a square without looking at the paper, and then ask me to conceive that your Italian, with the rope waiting for his neck, could draw the hand on the wall so firmly and truly, in the black shadow of that alley. It is absurd. By consequence, then, the hand was drawn early in the evening, long before any murder was committed; or else — mark this, Phillipps — it was drawn by some one to whom darkness and gloom were familiar and habitual; by some one to whom the common dread of the rope was unknown!

‘Again: a curious note was found in............