As a rule, the more bizarre a thing is the less mysterious it proves to be. It is your commonplace, featureless crimes which are really puzzling, just as a commonplace face is the most difficult to identify.

The lowest and vilest alleys of London do not present a more dreadful record of sin than does the smiling and beautiful countryside.

The more featureless and commonplace a crime is, the more difficult it is to bring it home.

A man should keep his little brain attic stocked with all the furniture that he is likely to use, and the rest he can put away in the lumber-room of his library, where he can get it if he wants it.

London, that great cesspool into which all the loungers of the Empire are irresistibly drained.

Mediocrity knows nothing higher than itself, but talent instantly recognizes genius.

It is a capital mistake to theorize before one has data.

How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?

When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking.

How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth.