[2] Set in 1920s Dublin in the aftermath of the Irish Civil War, the novel centers on "Gypo" Nolan.

Having disclosed the whereabouts of his friend Frankie McPhillip to the police for a reward, Gypo finds himself hunted by his revolutionary comrades for this betrayal.

Most famously, the novel was made into a film of the same name by John Ford in 1935 starring Victor McLaglen as Gypo Nolan.

The Informer later served as the basis for Jules Dassin's American drama Uptight, setting the story in the shadow of Martin Luther King Jr.'s assassination and adapting it to the American Civil Rights Movement.

An earlier film adaptation also named The Informer was directed by Arthur Robison in 1929.