The London retreat of Sherlock Holmes' brother Mycroft
"There are many men in London, you know, who, some from shyness, some from misanthropy, have no wish for the company of their fellows.
'Yet they are not averse to comfortable chairs and the latest periodicals.
'It is for the convenience of these that the Diogenes Club was started, and it now contains the most unsociable and unclubable men in town.
'No member is permitted to take the least notice of any other one. Save in the Stranger's Room, no talking is, under any circumstances, allowed, and three offences, if brought to the notice of the committee, render the talker liable to expulsion. My brother was one of the founders, and I have myself found it a very soothing atmosphere."
Holmes from 'The Greek Interpreter'.
The late Charles Gray and late Jeremy Brett as Messrs. Holmes and Holmes.
Although there is no hint in the original Sherlock Holmes canon that the Diogenes Club is anything but what it seems to be, several later writers have developed and made use of the idea that the club was founded as a front for the British secret service.
Although the club itself is not referred to in such a way in the original stories, this common supposition may have its root in the fact that Mycroft Holmes, in "The Adventure of the Bruce-Partington Plans," is revealed to be the supreme and indispensable brain-trust behind the British government, who pieces together the collective government secrets and then advises the best course of action. Given that Mycroft Holmes is established both as a co-founder of the club, and an indolent man who almost exclusively travels only between his home, his office, and the Club, this extrapolation would appear to be a logical one.
This idea was largely popularised by The Private Life of Sherlock Holmes, a 1970s motion picture directed by Billy Wilder, and has been frequently used in pastiches of Conan Doyle's original stories.
British fantasy writer Kim Newman has written a series of stories chronicling the activities of various agents of the Club (described in his stories as "an institution that quietly existed to cope with matters beyond the purview of regular police and intelligence services") throughout the 20th century, particularly in the 1920s, 1940s and 1970s.
In Newman's stories, the cases investigated by the Club are generally paranormal or occult in nature. The Diogenes Club is a central motif in several collections of Newman's stories, including Seven Stars (2000), where one mystery in particular is explored through many decades by generations of Diogenes-related investigators, The Man from the Diogenes Club (2006), featuring the 1970s agent Richard Jeperson, and The Secret Files of the Diogenes Club (2008).
A number of clubs today call themselves The Diogenes Club.