underneath the obvious. Yes; somebody has been saying something about
our client, and the thing that we have to find out is, what is it that
has been said and who has been saying it. We shall have to make a
pretext for another interview with Miss Gibson."

"By the way, why didn't you ask her what she meant?" I asked foolishly.

Thorndyke grinned in my face. "Why didn't you?" he retorted.

"No," I rejoined, "I suppose it is not politic to appear too discerning.
Let me carry the microscope for a time; it is making your arm ache, I
see."

"Thanks," said he, handing the case to me and rubbing his fingers; "it
is rather ponderous."

"I can't make out what you want with this great instrument," I said. "A
common pocket lens would do all that you require. Besides, a six-inch
objective will not magnify more than two or three diameters."

"Two, with the draw-tube closed," replied Thorndyke, "and the low-power
eye-piece brings it up to four. Polton made them both for me for
examining cheques, bank-notes and other large objects. But you will
understand when you see me use the instrument, and remember, you are to
make no comments."

We had by this time arrived at the entrance to Scotland Yard, and were
passing up the narrow thoroughfare, when we encountered a uniformed
official who halted and saluted my colleague.