fault they come to me, and I manage to
put them on the right scent. They lay all the evidence before me, and I
am generally able, by the help of my knowledge of the history of
crime, to set them straight. There is a strong family resemblance about
misdeeds, and if you have all the details of a thousand at your finger
ends, it is odd if you can't unravel the thousand and first. Lestrade
is a well-known detective. He got himself into a fog recently over a
forgery case, and that was what brought him here."

"And these other people?"

"They are mostly sent on by private inquiry agencies. They are
all people who are in trouble about something, and want a little
enlightening. I listen to their story, they listen to my comments, and
then I pocket my fee."

"But do you mean to say," I said, "that without leaving your room you
can unravel some knot which other men can make nothing of, although they
have seen every detail for themselves?"

"Quite so. I have a kind of intuition that way. Now and again a case
turns up which is a little more complex. Then I have to bustle about and
see things with my own eyes. You see I have a lot of special knowledge
which I apply to the problem, and which facilitates matters wonderfully.
Those rules of deduction laid down in that article which aroused your
scorn, are invaluable to me in practical work. Observation with me is
second nature. You appeared to be surprised when I told you, on our
first meeting, that you had come from Afghanistan."

"You were told, no doubt."

"Nothing of the sort. I _knew_ you came from Afghanistan. From long
habit the train of thoughts ran so swiftly through my mind, that I
arrived at the conclusion without being conscious of intermediate steps.
There were such steps, however. The train of reasoning ran, 'Here is a
gentleman of a medical type, but with the air of a military man. Clearly
an army doctor, then. He has just come from the tropics, for his face is
dark, and that is not the natural tint of his skin, for his wrists are
fair. He has undergone hardship and sickness, as his haggard face says
clearly. His left arm has been injured. He holds it in a stiff and
unnatural manner. Where in the tropics could an English army doctor have
seen much hardship and got his arm wounded? Clearly in Afghanistan.' The
whole train of thought did not occupy a second. I then remarked that you
came from Afghanistan, and you were astonished."

"It is simple enough as you expl