Marcello’s face cleared instantly.  Aurora had not told any one that he had quarrelled with his stepfather about her; that was quite evident, for there were not two more truthful people in the world than the Contessa and Kalmon, whose bright brown eyes were at that moment quietly studying his face.

“Not that the fact matters in the least,” said the Professor, resting his feet on the fender and exposing the broad soles of his wet walking-boots to the flame.  “The important fact is that the man has escaped, and we must catch him.”

“But how are you so sure that it was he that attacked me?  You cannot arrest a man on suspicion, without going through a great many formalities.  You cannot possibly have got an eye-witness to the fact, and so it must be a matter of suspicion after all, founded on a certain amount of rather weak circumstantial evidence.  Now, if it was he that tried to kill me, he failed, for I am alive, and perfectly well.  Why not let him alone, since I have got rid of him?”

“For a very good reason, which I think I had better not tell you.”

“Why not?”

“I am not sure what you would do if you were told it suddenly.  Are your nerves pretty good?  You used to be a delicate boy, though I confess that you look much stronger now.”

“You need not fear for my nerves,” Marcello answered with a short laugh.  “If they are sound after what I have been through in the last two years they will stand anything!”

“Yes.  Perhaps you had better know, though I warn you that what I am going to say will be a shock to you, of which you do not dream.”

“You must be exaggerating!” Marcello smiled incredulously.  “You had better tell me at once, or I shall imagine it is much worse than it is.”

“It could not be,” Kalmon answered.  “It is hard even to tell, and not only because what happened was in a distant way my fault.”

“Your fault?  For heaven’s sake tell me what the matter is, and let us be done with it!”

“Corbario wanted to get possession of your whole fortune.  That is why he tried to kill you.”

“Yes.  Is that all?  You have made me understand that already.”

“He had conceived the plan before your mother’s death,” said Kalmon.

“That would not surprise me either.  But how do you know it?”

“Do you remember that discovery of mine, that I called ’the sleeping death’?”

“Yes.  What has that to do with it?” Marcello’s expression changed.

“Corbario stole one of the tablets from the tube in my pocket, while I was asleep that night.”

“What?” Marcello began to grow pale.

“Your mother died asleep,” said Kalmon in a very low voice.

Marcello was transfixed with horror, and grasped the arms of his chair.  His face was livid.  Kalmon watched him, and continued.

“Yes.  Corbario did it.  Your mother used to take phenacetine tablets when she had headaches.  They were very like the tablets of my poison in size and shape.  Corbario stole into my room when I was sound asleep, took one of mine, and dropped in one of hers.  Then he put mine amongst the phenacetine ones.  She took it, slept, and died.”