“I confess,” said the colonel, “that even now I cannot see how it helps us.”

“It was the first link in my chain of reasoning. Powdered opium is by no means tasteless. The flavour is not disagreeable, but it is perceptible. Were it mixed with any ordinary dish the eater would undoubtedly detect it and would probably eat no more. A curry was exactly the medium which would disguise this taste. By no possible supposition could this stranger, Fitzroy Simpson, have caused curry to be served in the trainer’s family that night, and it is surely too monstrous a coincidence to suppose that he happened to come along with powdered opium upon the very night when a dish happened to be served which would disguise the flavour. That is unthinkable. Therefore Simpson becomes eliminated from the case, and our attention centres upon Straker and his wife, the only two people who could have chosen curried mutton for supper that night. The opium was added after the dish was set aside for the stable-boy, for the others had the same for supper with no ill effects. Which of them, then, had access to that dish without the maid seeing them?

“Before deciding that question I had grasped the significance of the silence of the dog, for one true inference invariably suggests others. The Simpson incident had shown me that a dog was kept in the stables, and yet, though someone had been in and had fetched out a horse, he had not barked enough to arouse the two lads in the loft. Obviously the midnight visitor was someone whom the dog knew well.

“I was already convinced, or almost convinced, that John Straker went down to the stables in the dead of the night and took out Silver Blaze. For what purpose? For a dishonest one, obviously, or why should he drug his own stable-boy? And yet I was at a loss to know why. There have been cases before now where trainers have made sure of great sums of money by laying against their own horses through agents and then preventing them from winning by fraud. Sometimes it is a pulling jockey. Sometimes it is some surer and subtler means. What was it here? I hoped that the contents of his pockets might help me to form a conclusion.

“And they did so. You cannot have forgotten the singular knife which was found in the dead man’s hand, a knife which certainly no sane man would choose for a weapon. It was, as Dr. Watson told us, a form of knife which is used for the most delicate operations known in surgery. And it was to be used for a delicate operation that night. You must know, with your wide experience of turf matters, Colonel Ross, that it is possible to make a slight nick upon the tendons of a horse’s ham, and to do it subcutaneously, so as to leave absolutely no trace. A horse so treated would develop a slight lameness, which would be put down to a strain in exercise or a touch of rheumatism, but never to foul play.”

“Villain! Scoundrel!” cried the colonel.

“We have here the explanation of why John Straker wished to take the horse out on to the moor. So spirited a creature would have certainly roused the soundest of sleepers when it felt the prick of the knife. It was absolutely necessary to do it in the open air.”

“I have been blind!” cried the colonel. “Of course that was why he needed the candle and struck the match.”