that leads into the place and with a groom on guard inside, and then gets out again in the same mysterious manner without having been seen or heard by a living soul.  In addition to all the windows being small and covered with a grille of iron, a fact which would make it impossible for anyone to get in or out once the doors were closed and guarded, Sir Henry himself will tell you that the stable has been ransacked from top to bottom, every hole and every corner probed into, and not a living creature of any sort discovered.  Yet only last night the groom, Tolliver, was set upon inside the place and killed outright in his efforts to protect the horse; killed, Cleek, with four men patrolling outside, and willing to swear—­each and every one of them—­that nothing and no one, either man, woman, child or beast, passed them going in or getting out from sunset until dawn.”

“Hum-m-m!” said Cleek, sucking in his lower lip.  “Mysterious, to say the least.  Was there no struggle?  Did the men on guard hear no cry?”

“In the case of the first groom, Murple, the one that was paralysed—­no,” said Sir Henry, as the question was addressed to him.  “But in the case of Tolliver—­yes.  The men heard him cry out, heard him call out ‘Help!’ but by the time they could get the doors open it was all over.  He was lying doubled up before the entrance to Black Riot’s stall, with his face to the floor, as dead as Julius Caesar, poor fellow, and not a sign of anybody anywhere.”

“And the horse?  Did anybody get at that?”

“No; for the best of reasons.  As soon as these attacks began, Mr. Cleek, I sent up to London.  A gang of twenty-four men came down, with steel plates, steel joists, steel posts, and in seven hours’ time Black Riot’s box was converted into a sort of safe, to which I alone hold the key the instant it is locked up for the night.  A steel grille about half a foot deep, and so tightly meshed that nothing bigger than a mouse could pass through, runs all round the enclosure close to the top of the walls, and this supplies ventilation.  When the door is closed at night, it automatically connects itself with an electric gong in my own bedroom, so that the slightest attempt to open it, or even to touch it, would hammer out an alarm close to my head.”

“Has it ever done so?”

“Yes—­last night, when Tolliver was killed.”

“How killed, Sir Henry?  Stabbed or shot?”

“Neither.  He appeared to have been strangled, poor fellow, and to have died in most awful agony.”

“Strangled?  But, my dear sir, that would hardly have been possible in so short a time.  You say your men heard him call out for help.  Granted that it took them a full minute—­and it probably did not take them half one—­to open the doors and come to his assistance, he would not be stone dead in so short a time; and he was stone dead when they got in, I believe you said?”

“Yes.  God knows what killed him—­the coroner will find that out, no doubt—­but there was no blood shed and no mark upon him that I could see.”