She faltered: "I don't think I understand."
"If you think it over, I feel sure you will," he suggested. "If your evidence is true, Fletcher was alive at one minute past ten."
"Yes," she said hesitantly. "Yes, of course he must have been."
"Yet at 10.02 the Constable saw an unknown man coming out of the garden-gate; and by 10.05 Fletcher was dead, and there was no trace to be found of his murderer."
"You mean it couldn't have happened?"
"Consider it for yourself, Mrs. North. If you say that the man you saw left at 9.58, who was the man the Constable saw?"
"How can I possibly tell?"
"Can you suggest any reason to account for his presence in the garden?"
"No, of course I can't. Unless he murdered Ernie."
"In considerably less than a minute?"