“It has everything to do with them,” declared the Doctor emphatically, “I repeat that if we grant these already stated premises concerning the composition of Mind and Matter, there can be no such thing as injustice.  Yet seemingly unjust things are done every day, and seemingly go unpunished.  I say ‘seemingly’ advisedly, because the punishment is always administered.  And here the ‘scientific ghosts’ come in.  ‘Vengeance is mine,’ saith the Lord,—­and the ghosts I speak of are the Lord’s way of doing it.”

“You mean ...” began Courtney.

“I mean,” continued the Doctor with some excitement, “that the sinner who imagines his sins are undiscovered is a fool who deceives himself.  I mean that the murderer who has secretly torn the life out of his shrieking victim in some unfrequented spot, and has succeeded in hiding his crime from what we call ‘justice,’ cannot escape the Spiritual law of vengeance.  What would you say,” and Dr. Dean laid his thin fingers on Courtney’s coat-sleeve with a light pressure,—­“if I told you that the soul of a murdered creature is often sent back to earth in human shape to dog its murderer down?  And that many a criminal undiscovered by the police is haunted by a seeming Person,—­a man or a woman,—­who is on terms of intimacy with him,—­who eats at his table, drinks his wine, clasps his hand, smiles in his face, and yet is truly nothing but the ghost of his victim in human disguise, sent to drag him gradually to his well-deserved, miserable end; what would you say to such a thing?”

“Horrible!” exclaimed Courtney, recoiling.  “Beyond everything monstrous and horrible!”

The Doctor smiled and withdrew his hand from his companion’s arm.

“There are a great many horrible things in the universe as well as pleasant ones,” he observed dryly.  “Crime and its results are always of a disagreeable nature.  But we cannot alter the psychic law of equity any more than we can alter the material law of gravitation.  It is growing late; I think, if you will excuse me, I will go to bed.”

Courtney look at him puzzled and baffled.

“Then your ‘scientific ghosts’ are positive realities?” he began; here he gave a violent start as a tall white figure suddenly moved out of the shadows in the garden and came slowly towards them.  “Upon my life, Doctor, you have made me quite nervous!”

“No, no, surely not,” smiled the Doctor pleasantly—­“not nervous!  Not such a brave killer of game as you are!  No, no!  You don’t take Monsieur Armand Gervase for a ghost, do you?  He is too substantial,—­far too substantial!  Ha! ha! ha!”

And he laughed quietly, the wrinkled smile still remaining on his face as Gervase approached.

“Everybody is going to bed,” said the great artist lazily.  “With the departure of the Princess Ziska, the pleasures of the evening are ended.”

“She is certainly the belle of Cairo this season,” said Courtney, “but I tell you what,—­I am rather sorry to see young Murray has lost his head about her.”