Ex-Professor Moriarty of mathematical celebrity... is the Napoleon of crime, Watson.

Excellent!" I cried. "Elementary," said he.

Once or twice in my career I feel that I have done more real harm by my discovery of the criminal than ever he had done by his crime. I have learned caution now, and I had rather play tricks with the law of England than with my own conscience.

Of all ghosts the ghosts of our old loves are the worst.

As a rule, the more bizarre a thing is, the less mysterious it proves to be.

I cannot live without brainwork. What else is there to live for? Stand at the window here. Was ever such a dreary, dismal, unprofitable world? See how the yellow fog swirls down the street and drifts across the duncoloured houses. What could be more hopelessly prosaic and material?

A client is to me a mere unit, a factor in a problem.