“I have given you my word. What further proof do you want?”

“I must remain alone in this room.”

“I do not understand,” I said, with surprise.

“It’s an idea that occurred to me when reading your article. Certain details established an extraordinary coincidence with another case that came under my notice. If I am mistaken, I shall say nothing more. And the only means of ascertaining the truth is by my remaining in the room alone.”

What was at the bottom of this proposition? Later, I recalled that the man was exceedingly nervous; but, at the same time, although somewhat astonished, I found nothing particularly abnormal about the man or the request he had made. Moreover, my curiosity was aroused; so I replied:

“Very well. How much time do you require?”