“Why should he do that?”

“Because he heard something from the woods, or saw something.”

“The wood is very dense between here and the road. It is not possible to see this spot from the road, and although the road is not far away, it is too far, in my opinion, for any but the loudest of sounds to be heard there. Besides, this speculation is superfluous, for I have made a very wide sweep of the whole area around this glade, and there is not a single footprint anywhere about, not one. Believe me, Gregson, when I say I would stake my reputation – my entire life’s work – on it!”

“If you say so, Mr Holmes,” said Gregson after a moment, “then that is good enough for me. But do you realize where your argument leads? We have two men murdered in this isolated spot, and yet we have, according to you, not three sets of footprints leading here, as I had first expected to find, being those of Palfreyman, Martin and their murderer, nor yet two sets of prints, which according to my later theory would be those of Palfreyman and Martin, but only one set of prints. It is completely impossible! Indeed, it is not only impossible, it is absurd!”

“Yes,” said Holmes, in a dry tone. “It does appear on the face of it to be impossible. You’re a good man, Gregson, one of the best, and I have gone carefully through all the evidence, so that when I tell you what really happened here, you will understand and believe me. With a lesser man, I probably shouldn’t have bothered.”

Inspector Gregson took a small cigar from his waistcoat pocket, struck a match and lit it. “Go on,” he said. “I am still all ears.”

“Very well,” said Holmes. “What we have here is a clear case of murder.”

“Well, yes, of course,” returned Gregson. “We know that Professor Palfreyman murdered young Martin. As you yourself agreed, the professor shot him with his pistol.”

Holmes shook his head. “No,” said he, “you have it the wrong way about. Palfreyman did not murder Martin. On the contrary, Martin murdered Palfreyman.”

“What!”

“It is one of the most callous, calculated, cold-blooded murders I have ever encountered. What you see here before you is, apart, of course, from his own death, the culmination of Martin’s scheme for murder which I believe he planned many months ago.”

“You amaze me, Holmes!” I cried. “I cannot believe what you are saying! How on earth do you arrive at that conclusion?”

“I will tell you my reasoning, Watson, and you can see if you can find any flaw in it. First, let us return to the matter of the footprints. As you remarked, Gregson, the fact that there appeared to be but one set of footprints leading here seemed an impossibility. There is, however, one way in which it could have come about, and that is if one of the two men was in fact carrying the other. Now, in what circumstances might that occur? Surely only if one of them was incapacitated, probably by being unconscious.

“I had noted the single set of footprints earlier, when the three of us first came along the path, but gave it little thought at first. I assumed the footprints were those of the professor, and the fact that there were prints leading into the wood, but none coming back, suggested that – unless he had gone further afield – we might find him sitting smoking his pipe in the woods, as Miss Calloway had told us he often did. Then, however, I noticed an odd thing: the footprints in question were unusually deep – much deeper than either Dr Watson’s or my own – with the heels especially marked. This suggested that the man that made them was carrying an exceptionally heavy burden of some sort. My attention having been drawn to this curious feature, I then observed that although, to judge by his shoe size, the man was of roughly average stature, the footprints were often much closer together than one would expect, which also suggested that he was struggling with a heavy burden.

“When we reached this clearing, and found the two dead men, I examined their shoes and established that the footprints on the path had been made by Martin. There were no other footprints anywhere about in the woods surrounding the clearing, so it was evident that, as I suspected by then, Martin had carried the professor here. The more I considered the matter, the more it seemed crystal clear that Martin had intended to murder the professor by hanging, to make it appear to have been a case of suicide. Martin had often visited Bluebell Cottage, and would be familiar with the routine of the household, so he would know that the cook always went over to Norwood to see her sister on Wednesday morning. When Miss Calloway told him that she was going to consult me this morning, he would have realized that there would be no one but the professor in the house, and he would thus have the opportunity he needed to put his evil scheme into effect. He must therefore have called in at the cottage on some pretext or other, and been let in by the professor himself. But how did he manage to subdue the professor in order to get him out here? Clearly, by striking him on the back of the head, probably as the professor sat at his desk. This is what would have caused that very severe wound to the professor’s head, which simply falling over and banging his head on that stone over there could never have done.

“What I think must have happened when they reached the clearing here is that Martin dropped the professor to the ground while he rigged up that noose on the branch of the tree. But the professor, who was, in a sense, dying at that moment, and would probably not have lived another ten minutes under any circumstances, must have regained consciousness sufficiently to see what Martin was doing. When Martin turned back to him, the professor had drawn his pistol – it is very small and weighs little, which would explain why Martin failed to notice that it was in the professor’s jacket pocket – and shot his assailant with it at point-blank range. The recoil and the burn on his hand made him fling the gun to one side and stagger backwards, where he fell to the ground and struck his head on that stone, which finished him off. It is because he was so severely injured, and probably scarcely conscious, that he was unable to break his fall. He may even have been dead before his body struck the ground. Therefore, to sum up: Martin murdered Palfreyman, and although Palfreyman undoubtedly shot and killed Martin, that was not, legally speaking, an act of murder, as he was acting in self-defence. That, I believe, is what happened.”

We sat in silence for some time after Holmes had finished speaking. If his analysis was correct, what had happened here in this quiet woodland glade seemed both too terrible and too fantastic to contemplate, yet I felt sure that, on the evidence, he must be right.

“If you require any further proof of the truth of my view,” said Holmes after a few moments, “then you could look in Martin’s jacket pocket. He trimmed the rope with which he made the noose, and there is a small length of the rope in his pocket, along with a sharp jack-knife. There is also a mark of blood on the back of his jacket, near the shoulder, which must have come from the professor’s wound when he was being carried out here. I also took a look in the professor’s study, to see if there was any evidence there to support my theory that it was there that Martin had attacked the professor, and found among the disorder that the poker in the hearth is smeared with blood and hair. That is clearly the murder weapon. I have left it where it was, in the hearth, for you to see, Gregson. No doubt Martin left the kitchen door unlocked because he intended to return to the house to tidy up the study and conceal what had happened there.”

“But surely,” said Gregson, “if Martin’s scheme had succeeded, and we had found the professor hanged here in the woods, our suspicions as to what had really happened would have been instantly aroused by that savage wound on the back of his head. Martin could not have supposed that we would not notice that!”