The Man Who Was Thursday: A Nightmare by G. K. Chesterton

In a surreal turn-of-the-century London, Gabriel Syme, a poet, is recruited to a secret counter-terrorist taskforce at Scotland Yard. Syme persuades Lucian Gregory, an anarchist, to lead him to the local terrorist cell, where he is elected as the cell's representative to the worldwide council of anarchists — the Central Anarchist Council — seven men, each using the name of a day of the week as a code name. His efforts to thwart the council's intentions and oppose all anarchic acts reveal a comical number of unlikely allies. Ultimately, Syme and his fellow champions of order confront the head anarchist, only to find their perception of order and chaos turned completely upside down. The novel's subtitle, "A Nightmare," is a summation of the frightening and increasingly surreal world in which Syme finds himself enmeshed.