I'll nominate
The Club of Queer Trades by G. K. Chesterton.
From the blurb on the Penguin Edition:
"A master of the tongue in cheek, G.K. Chesterton's ingenious and, above all, paradoxical stories introduce Basil Grant, a sleuth so finely portrayed as to rival Sherlock Holmes. Eschewing facts for physiognomy, deduction for intuition, method for madness, he moves unerringly to his goal.
"Accompanied by the gullible narrator of the tales and an excitable private detective, Basil Grant deals with a lethal message written in pansies, a professor's insanity, a country vicar's predicament and other puzzling situations, all of which lead them to the same source . . . .
"While each story is complete in itself, together they weave another mystery which leads to its own climax . . . ."
The six classic stories taken together occupy only 126 pages in the Penguin edition.
It is available free from Project Gutenberg and in both a free and very cheap Kindle edition in Amazon {and on Feedbooks} as well as being included in many ebook collections devoted to Chesterton.
http://www.amazon.co.uk/s/ref=nb_sb_...k%3AThe+Club+o