I replied in the negative, but not as decidedly as I might have done. I remembered my impression that the stranger’s voice was not unfamiliar to me. I explained this rather haltingly to the inspector.

“It was a rough, uneducated voice, you say?”

I agreed, but it occurred to me that the roughness had been of an almost exaggerated quality. If, as the inspector thought, the man had wished to hide his face, he might equally well have tried to disguise his voice.

“Do you mind coming into the study with me again, doctor? There are one or two things I want to ask you.”

I acquiesced. Inspector Davis unlocked the door of the lobby, we passed through, and he locked the door again behind him.

“We don’t want to be disturbed,” he said grimly. “And we don’t want any eavesdropping either. What’s all this about blackmail?”

“Blackmail!” I exclaimed, very much startled.