But beyond that my memory gets a bit sketchy. My vague recollection is that this is the story of two poets: Lucian Gregory, an anarchist hiding in plain sight; and Gabriel Syme, recruited by Scotland Yard to pose as an anarchist and infiltrate the secretive (and oxymoronic) Central Anarchist Council under the code name Thursday.
The story alone is quite entertaining, but Chesterton adds some interesting statements about the nature of the apparent chaos of the universe. Contrary to what anarchists and existentialists would have us believe, Chesterton makes the point that mere chance doesn't have any real bearing on our lives--that all life is dictated by divinely inspired order.
And that's as far as my memory goes (without delving into spoilers, anyway). Not much of a review, I know, but it's the best a literary amnesiac can do. At least I can leave you with a couple of quotes that struck me by their peculiar expressiveness:
"The young man with the long, auburn hair and the impudent face--that young man was not really a poet; but surely he was a poem."
"This particular evening, if it is remembered for nothing else, will be remembered in that place for its strange sunset. It looked like the end of the world."