Gabriel Syme, a poet and undercover detective, infiltrates a council of seven anarchists who each adopt the name of a day of the week. Syme finds himself elected as 'Thursday' and must navigate a labyrinthine conspiracy where the lines between law enforcement and subversion blur. As he attempts to dismantle the organization from within, he discovers that his fellow anarchists are not what they appear to be. The narrative follows a surreal, dream-like progression through London, challenging the protagonist's perception of reality and authority.

Discussion often centers on the book's unique blend of detective fiction and metaphysical inquiry. Readers frequently highlight the disorienting, dream-like atmosphere that permeates the narrative, which serves to amplify the philosophical questions posed by the author. Critics often note the balance between the fast-paced, thriller-like plot and the underlying theological debates regarding the nature of evil and divine order. The work is frequently analyzed for its commentary on the anxieties of the early twentieth century, specifically regarding political radicalism and social stability. Many readers find the conclusion particularly provocative, as it shifts the tone from a standard mystery to a profound meditation on human existence.