“We have now to deal with the detective, and here again there was nothing to associate his death with the bed of the Borgia.  Yet you will see without my aid how easily he came by his death.  Peter Hardcastle desires to be alone, that he may study the Grey Room and everything in it.  He is left as he wishes, walks here and there, sketches a ground plan of the room and exhausts its more obvious peculiarities.  Would that he had known the meaning of the golden bull!  Presently he strikes a train of thought and sits down to develop it.  Or he may not have finished with the room and have taken a seat from which he could survey everything around him.  He sits at the foot of the bed—­there on the right side.  He makes his notes, then his last thoughts enter his mind—­abstract reflection on the subject of his trade.  For a moment he forgets the matter immediately in hand and writes his ideas in his book.  He has been sitting on the bed now for some while—­how long we know not, but long enough to create the heightened temperature which is all the watchful fiend within the mattress requires to summon him.  Then ascends the spirit of death, and Hardcastle, surprised as Captain May was surprised, leaps to his feet.  He takes two or three steps forward; his book and pen fall from his hand and he drops upon his face—­a dead man.  He is, of course, still warm when Mr. Lennox finds him; but the bed he leaped from is cold again and harmless—­its work done.

“There remains the priest, the Rev. Septimus May.  He neither lay on the bed, nor sat upon it.  But what did he do?  He clearly knelt beside it a long time, engaged in prayer.  Nothing more natural than that he should stretch his arms over the mattress; bury his face in his hands, and so remain in commune with the Almighty, uttering petition after petition for the being he conceived as existing in the Grey Room, without power to escape from it.  Thus leaning upon the bed with his arms stretched upon it and his head perhaps sunk between them, he presently creates that heightened temperature sufficient to arouse the destroyer.  It enters into him—­how, we know not yet—­and he sinks unconscious to the floor, while the bed is quickly cold again.

“As to the four detectives—­Inspector Frith and his men—­pure chance saved the life of at least one of them, and by so doing, chance also prevented them from discovering that the bed in their midst was the seat of all the trouble.  Had one among them taken up his watch upon it, he would certainly have died in the presence of his collaborators; but the men sat on chairs in the corners of the room, and the chairs were harmless.  Whether their gas masks would indeed have saved them remains, of course, to be proved.  I doubt it.

“Such, my friends, were the masterpieces of the Borgia, for whom the profoundest chemists worked willingly enough and by doing so doubtless made their fortunes.  Their poisons were so designed to act that, by their very operation, the secrets of them were concealed, and all clues obliterated.  Chemistry knows nothing of the supernatural, yet can, as in this case, achieve results that may well appear to be black magic.