understand what that is. Here in London we have lots of
Government detectives and lots of private ones. When these
fellows are at 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.