He spoke the truth. I, who was using the telephone all day, entirely agreed with him.

"Well, Preston, it was a skillful imitation and not my voice at all."

"If you will excuse me, Sir Thomas," he replied, "your voice is a very distinctive one. It's not very easily mistaken by any one who has heard your voice once or twice."

"That only makes the thing the more mysterious."

"The more easy, I should say, Sir Thomas. It must be far less difficult to imitate an outstanding voice with marked peculiarities than an ordinary one."

He was right there, it hadn't occurred to me before.

"But who in the office would dare to imitate my voice?"

"That, of course, I could not say, Sir Thomas, but we've only the word of the unknown person who rang me up that he was speaking from the office. For all we know he might have been in the next flat."

That again was a point and I noted it.

"I'm not going to waste any time," I said. "I'll go down to the office at once and see if I can find out anything."