As a child, the unnamed narrator of The Third Policeman was sent to boarding school on the death of both his parents. As a young adult, he returns to his hometown, where the meager family farm has been suspiciously mismanaged by a lazy bachelor named John Divney. The fantastic events of the novel, and the narrator’s own relation of his story, begin with the murder of a wealthy old man, Phillip Mathers, by the narrator in the company, and at the instigation, of Divney. While the narrator buries the corpse, Divney hides the cash box they sought. Months later, the pair return to recover the money, at which point the narrator, betrayed by Divney, becomes aware of eerie changes in his surroundings and in his perception of them.
For what appears to be three days, the narrator seeks Divney and the cash box, protests his innocence under police interrogation, and escapes from the police as they plan a scaffold for his execution. Throughout these episodes, the narrator endures a comical but profound disorientation of ordinary experience: Buildings appear to be two-dimensional, bicycles seem alive, and the sun apparently rises and sets in the east. He negotiates these baffling phenomena by adducing quite seriously the baroque and ludicrous metaphysics of a fictional philosopher named de Selby. The absurdity of the narrator’s scholarship is matched by that of the policemen, who are doctrinaire concerning theories about the source of all sickness in teeth, colors in winds, night as a material substance, and the slow but inexorable molecular exchange between bicycles and the persons riding them.
At last, aided by the third policeman, Fox, the narrator locates Divney and is startled to find him now the father of an adolescent son. In a fatal apoplectic fit at the sight of the narrator, Divney confesses to having murdered his co-conspirator when they returned for Mathers’ money box. Throughout the story, the narrator has been dead, and elapsed time is revealed to have been not three days but sixteen years. The novel ends with the narrator and Divney, now both dead, now both known to be murderers, beginning to repeat the novel’s course of events, now seen as a comic and fantastic vision of the afterlife.