Marcello gasped for breath, his eyes starting from his head.

“You see,” Kalmon went on, “it was long before I found that my tablets had been tampered with.  There had been seven in the tube.  I knew that, and when I glanced at the tube next day there were seven still.  The tube was of rather thick blue glass, if you remember, so that the very small difference between the one tablet and the rest could not be seen through it.  I went to Milan almost immediately, and when I got home I locked up the tube in a strong-box.  It was not until long afterwards, when I wanted to make an experiment, that I opened the tube and emptied the contents into a glass dish.  Then I saw that one tablet was unlike the rest.  I saw that it had been made by a chemist and not by myself.  I analysed it and found five grains of phenacetine.”

Marcello leaned back, listening intently, and still deadly pale.

“You did not know that I was trying to find out how you had been hurt, that I was in communication with the police from the first, that I came to Rome and visited you in the hospital before you recovered your memory.  The Contessa was very anxious to know the truth about her old friend’s son, and I did what I could.  That was natural.  Something told me that Corbario had tried to kill you, and I suspected him, but it is only lately that I have got all the evidence we need.  There is not a link lacking.  Well, when I came to Rome that time, it chanced that I met Corbario at the station.  He had come by the same train, and was looking dreadfully ill.  That increased my suspicion, for I knew that his anxiety must be frightful, since you might have seen him when he struck you, and might recognise him, and accuse him.  Yet he could not possibly avoid meeting you.  Imagine what that man must have felt.  He tried to smile when he saw me, and said he wished he had one of those sleeping tablets of mine.  You understand.  He thought I had already missed the one he had taken, though I had not, and that he had better disarm any possible suspicion by speaking of the poison carelessly.  Then his face turned almost yellow, and he nearly fainted.  He said it was the heat, and I helped him to his carriage.  He looked like a man terrified out of his senses, and I remembered the fact afterwards, when I found that one tablet had been stolen; but at the time I attributed it all to his fear of facing you.  Now we know the truth.  He tried to murder you, and on the same day he poisoned your mother.”

Kalmon sat quite still when he had finished, and for a long time Marcello did not move, and made no sound.  At last he spoke in a dull voice.

“I want to kill him myself.”

The Professor glanced at him and nodded slowly, as if he understood the simple instinct of justice that moved him.

“If I see him, I shall kill him,” Marcello said slowly.  “I am sure I shall.”

“I am afraid that he has escaped,” Kalmon answered.  “Of course there is a possibility that he may have had some object in deceiving your coachman by driving to the railway station, but it is not at all likely.  He probably took the first train to the north.”