ird party. That expression of
hers, 'speaking from my own observation,' seemed to imply that her
observations of him were not in entire agreement with somebody else's."

"Good man!" exclaimed Thorndyke, slapping me on the back, to the
undissembled surprise of a policeman whom we were passing; "that is what
I had hoped for in you--the capacity to perceive the essential
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.

"Ah, I thought we should see you here before long, doctor," said he
genially. "I heard this morning that you have this thumb-print case in
hand."

"Yes," replied Thorndyke; "I am going to see what can be done for the
defence."

"Well," said the officer as he ushered us into the building, "you've
given us a good many surprises, but you'll give us a bigger one if you
can make anything of this. It's a foregone conclusion, I should say."

"My dear fellow," said Thorndyke, "there is no such thing. You mean that
there is a _prima facie_ case against the accused."

"Put it that way if you like," replied the officer, with a sly smile,
"but I think you will find this about the hardest nut you ever tried
your teeth on--and they're pretty strong teeth t