The story opens with a discussion between Gregory and Syme, who discuss the nature of poetry. Gregory is an anarchist, and he believes that poetry is about revolt, whereas Syme insists that order is all and that the railroad timetable is man's most poetical creation. Later Gregory invites Syme for a drink. The table they're sitting at suddenly descends underground to the secret meeting place of an anarchist council, and then it gets weird. Each member of the council has taken the name of a day of the week, hence the book's title (which I love, by the way). It turns out that Syme is a policeman, and he gets himself elected head of the council.
Lots of action follows: sword fights, balloon escapes, chases on horseback, elephantback escapes, and more. What's revealed about the council and its members is best not mentioned here. You need to find that out for yourself.
Christian allegory, metaphysics, adventure, fantasy, action, and more. This book has it all. Not for everybody, I suspect, but check it out and give it a chance.