“And yet,” he went on, in cold, sinister accents, “let him take but a small pinch of this, and no one need fear his tyranny again in this world.  No one is much afraid of a man who lies some six feet under ground, shut up in a strong oak coffin, with a finely carved gravestone over his head.”

He stopped short, and fixed his keen eyes upon the agitated girl, who stood in front of him.  For at least two minutes the man and the girl stood face to face, motionless, and without exchanging a word.  Through the dead, weird silence, the pulsations of their hearts were plainly audible.  It seemed as if before speaking again each wished to fathom the depths of guilt that lay in the other’s heart.  It was a compact entered into by look and not by speech; and Daumon so well understood this, that at length, when he did speak, his voice sank to a hoarse whisper, as though he himself feared to listen to the utterance of his own thoughts.

“A man taking this feels no pain.  It is like a heavy, stunning blow on the forehead—­in ten seconds all is over, no gasp, no cry, but the heart ceases to beat forever; and, best of all, it leaves no trace behind it.  A little of this, such a little, in wine or coffee, would be enough.  It is tasteless, colorless, and scentless, its presence is impossible to be detected.”

“But in the event of a post-mortem examination?”

“By skilful analysts in Paris or the larger towns, there would be a chance; but in a place like this, never!  Never, in fact, anywhere, unless there had been previous grounds for suspicion.  Otherwise only apoplectic symptoms would be observed; and even if it was traced there comes the question, By whom was it administered?”

He stopped short, for a word rose to his lips which he did not dare utter; he raised his hands to his mouth, coughed slightly, and went on,—­

“This substance is not sold by chemists; it is very rarely met with, difficult to prepare, and terribly expensive.  The smallest quantity might be met with in the first-class laboratories for scientific purposes, but it is most unlikely for any one in these parts to possess any of this drug, or even to know of its existence.”

“And yet you——­”

“That is quite another matter.  Years ago, when I was far away from here, it was in my power to render a great service to a distinguished chemist, and he made me a present of this combination of his skill.  It would be impossible to trace this bottle; I have had it ten years, and the man who gave it to me is dead.  Ten years?  No, I am wrong, it is now twelve.”

“And in all these years has not this substance lost any of its destructive powers?”

“I tried it only a month ago.  I threw a pinch of it into a basin of milk and gave it to a powerful mastiff.  He drank the milk and in ten seconds fell stark and dead.”

“Horrible!” exclaimed Diana, covering her face with her hand, and recoiling from the tempter.