The Third Policeman by Flann OBrien

The Third Policeman follows a narrator who is obsessed with the work of a scientist and philosopher named de Selby (who believes that Earth is not round but sausage-shaped)—and has finally completed what he believes is the definitive text on the subject. But, broke and desperate for money to get his scholarly masterpiece published, he winds up committing robbery—and murder.

From here, this remarkably imaginative dark comedy proceeds into a world of riddles, contradictions, and questions about the nature of eternity as our narrator meets some policemen with an obsession of their own (specifically, bicycles), and engages in an extended conversation with his dead victim—and his own soul, which he nicknames Joe.