Did not the stationmaster see a third David Hume leave the station that day when the movements of only two are known to us.

What became of this third personage during the afternoon?
Where did he change into evening dress?
Why did Sir Alan leave documents of such grave importance in so insecure a hiding-place ?" "There is no use in asking me questions I can't answer," snapped the detective.
"Perhaps not.

I think you said that you amused yourself in your Middle Street lodgings by taking to pieces a small electrical machine fitted together by your companion ?" "Yes, sir; but what of that ?" "Let us suppose that, instead of a complex machine he built a small arch of toy bricks, and you were well acquainted with the model whilst each brick was numbered in rotation, don't you think you could manage to reconstruct the arch after repeated efforts ?" "I expect so." "Well, my dear Winter, we have now got together every material stone in our edifice.

Mrs.Capella's yielding to blackmail is the keystone of the arch.

Every loose block fits at once into its proper place.