The paper was covered with the tracings of the footmarks of some small animal. It had five well-marked footpads, an indication of long nails, and the whole print might be nearly as large as a dessert-spoon.

“It’s a dog,” said I.

“Did you ever hear of a dog running up a curtain? I found distinct traces that this creature had done so.”

“A monkey, then?”

“But it is not the print of a monkey.”

“What can it be, then?”

“Neither dog nor cat nor monkey nor any creature that we are familiar with. I have tried to reconstruct it from the measurements. Here are four prints where the beast has been standing motionless. You see that it is no less than fifteen inches from fore-foot to hind. Add to that the length of neck and head, and you get a creature not much less than two feet long -probably more if there is any tail. But now observe this other measurement. The animal has been moving, and we have the length of its stride. In each case it is only about three inches. You have an indication, you see, of a long body with very short legs attached to it. It has not been considerate enough to leave any of its hair behind it. But its general shape must be what I have indicated, and it can run up a curtain, and it is carnivorous.”

“How do you deduce that?”

“Because it ran up the curtain. A canary’s cage was hanging in the window, and its aim seems to have been to get at the bird.”

“Then what was the beast?”

“Ah, if I could give it a name it might go a long way towards solving the case. On the whole, it was probably some creature of the weasel and stoat tribe - and yet it is larger than any of these that I have seen.”

“But what had it to do with the crime?”

“That, also, is still obscure. But we have learned a good deal, you perceive. We know that a man stood in the road looking at the quarrel between the Barclays - the blinds were up and the room lighted. We know, also, that he ran across the lawn, entered the room, accompanied by a strange animal, and that he either struck the colonel or, as is equally possible, that the colonel fell down from sheer fright at the sight of him, and cut his head on the corner of the fender. Finally we have the curious fact that the intruder carried away the key with him when he left.”

“Your discoveries seem to have left the business more obscure than it was before,” said I.

“Quite so. They undoubtedly showed that the affair was much deeper than was at first conjectured. I thought the matter over, and I came to the conclusion that I must approach the case from another aspect. But really, Watson, I am keeping you up, and I might just as well tell you all this on our way to Aldershot to-morrow.”

“Thank you, you have gone rather too far to stop.”

“It is quite certain that when Mrs. Barclay left the house at half-past seven she was on good terms with her husband. She was never, as I think I have said, ostentatiously affectionate, but she was heard by the coachman chatting with the colonel in a friendly fashion. Now, it was equally certain that, immediately on her return, she had gone to the room in which she was least likely to see her husband, had flown to tea as an agitated woman will, and finally, on his coming in to her, had broken into violent recriminations. Therefore something had occurred between seven-thirty and nine o’clock which had completely altered her feelings towards him. But Miss Morrison had been with her during the whole of that hour and a half. It was absolutely certain, therefore, in spite of her denial, that she must know something of the matter.