‘The Man Who Was Thursday: a Nightmare’ is a novel written by G.K. Chesterton in 1908. It is a very complex work, but its characteristic traits are those of the genre thriller , detective , noir.In this work Chesterton talks a lot about the concept of Anarchy, understood in a rather intimate and non-political sense.His relationship with life and God is narrated through a raw conflict. The British writer engages in a real inner battle with God.The novel is set in London at the beginning of the 1900s and Gabriel Syme is an agent of Scotland Yard, recruited in an anti-anarchist task force. Lucian  Gregory, on the other hand, is a declaredly anarchist poet who lives in the suburbs of Saffron Park. A casual meeting between Gabriel and Lucian (at an event) upsets the lives of both. Here begins the intricate, intriguing and mysterious adventure full of action, conspiracies and twists.