The poet Gabriel Syme investigates within the anarchist milieu for the London police. He manages to infiltrate an anarchist circle whose leading members are named after the days of the week. As Thursday, Syme rises to the top leadership. There, he meets the leader Sunday and soon becomes embroiled in a series of grotesque and fantastical adventures. As is typical of Gilbert Keith Chesterton, a metaphysical dimension soon becomes apparent in this turbulent detective novel, as the weekday anarchists reveal themselves to be archangels in the battle against the "playing God" Sunday.