Villebois opened the door and beckoned to him to come in. Riche had taken the commissaire's conduct so much to heart that at first he refused to answer.
"A thousand pardons, M. le docteur, for appearing so rude," said the commissaire in a very apologetic tone, "but I understand that you are able to give some clue to this assassination?"
Dr. Riche, seeing that M. Biron's apology was sincere, slowly thawed and became more amiable.
"Yes, monsieur," he replied, "I came downstairs during the fire to look after the professor, who was fast asleep on a couch, and just as I was about to enter the chamber, the door was shut in my face and locked. When I entered the room the bird had flown, but I picked up a hypodermic syringe half full of liquid, from the floor."
"But didn't you try to find the fellow?"
"Of course I did. I ran round the house into the street, and on arriving at the first corner I saw a man entering a cab, but he was half inside, and too far away for me to recognise who he was. I ran as hard as I could, and shouted to the cocher, but he lashed his horse into a gallop and disappeared. When I returned to the house I searched the room again, and found the broken injection needle on the floor, and guessing that there was some connection between this needle and Professor Delapine's condition, I examined him and discovered that life was extinct."
"Excellent, excellent," said the commissaire, delighted, and rubbing his hands together as if he had heard a good story.
"Parbleu," he cried, "but, mon ami, this is exceedingly interesting, perfectly romantic. Ah, mon cher docteur, our task grows more and more delightful. I must instruct my attendants this instant," and excusing himself he ran off as fast as his little legs could carry him. In the midst of his haste, however, a sudden thought struck him, and he returned to Dr. Villebois, and taking him on one side asked:
"Can you tell me, doctor, what was the cause of the fire?"
"It was undoubtedly a case of arson," replied Villebois and Riche together.