In Libria, emotion is outlawed. The Tetragrammaton Clerics are the elite arm of its law enforcement, tasked with tracking down any materials likely to incite emotion to destroy them, and to terminate “sense offenders”, that is, any citizens that have broken the law by feeling emotion.
John Preston (Christian Bale) is Libria’s highest ranking Grammaton Cleric. His Call to Adventure comes when he discovers that his partner, Errol Partridge (Sean Bean), has confiscated a book of poems under false pretenses. Tracking him to a ruined cathedral in the Nethers (an area of cities destroyed by a Third World War), he finds him reading the book, and unapologetically so. As Partridge is now guilty of sense offending, Preston executes him.
The event seems to shake Preston from a proscribed routine just enough that he accidentally breaks a vial of his morning dose of Prozium, and he begins to feel emotions.