The Man Who Was Thursday, A Nightmare - G. K. Chesterton

In a surreal turn-of-the-century London, Gabriel Syme, a poet, is recruited to a secret anti-anarchist taskforce at Scotland Yard. Lucian Gregory, an anarchist poet, is the only poet in Saffron Park, until he loses his temper in an argument over the purpose of poetry with Gabriel Syme, who takes the opposite view. After some time, the frustrated Gregory finds Syme and leads him to a local anarchist meeting-place to prove that he is a true anarchist. Instead of the anarchist Gregory getting elected, the officer Syme uses his wits and is elected as the local representative to the worldwide Central Council of Anarchists. The Council consisting of seven men, each using the name of a day of the week as a code name; Syme is given the name of Thursday... (Summary from Wikipedia)