“I can assure you, Dr. Priestley, that at that moment there was nobody in sight but Mr. Copperdock and myself,” replied Mr. Ludgrove simply.

“Thank you,” said the Professor. “Now, I am prepared to examine the evidence you have to show me.”

Mr. Ludgrove rose from his chair. “Will you excuse me for a few minutes, Dr. Priestley?” he said. “Before I begin my explanation, I should like to fetch certain things which I have put in a place of security upstairs. I will not keep you very long.”