'This affair must all be unravelled from within.' He tapped his forehead. 'These little grey cells. It is 'up to them' - as you say over here.'

I am not keeping back facts. Every fact that I know is in your possession. You can draw your own deductions from them.

I did not deceive you, mon ami. At most, I permitted you to deceive yourself.

Every murderer is probably somebody's old friend.

His peculiar gift was the power of holding continuously in his mind a purely mental problem until he had seen it through.

It is the mark of an educated mind to be able to entertain a thought without accepting it.

The right method in any particular case must be largely determined by the nature of the problem.