Established by survivors of World War III, the totalitarian city-state of Libria blames human emotion as the root of all conflicts. It strictly outlaws all activities or objects that stimulate emotion, with violators labeled Sense Offenders and sentenced to death. The population has to take a daily injection of the emotion-suppressing drug called Prozium II. Libria is governed by the Tetragrammaton Council, led by "Father", who communicates propaganda through giant video screens. The police force is led by the Grammaton Clerics, elite fighters trained in the art of gun kata. Clerics frequently raid homes to search for and destroy illegal materials – art, literature and music – executing violators on the spot. A resistance movement, known as the "Underground", emerges to topple Father and the Tetragrammaton Council.
The flag of Libria. The four Ts on the flag represent the Tetragrammaton Council.In 2072, John Preston is a high-ranking Cleric whose wife, Viviana, was executed as a Sense Offender, leaving him as a single parent of two. Following a raid, Preston's partner Errol Partridge saves a book of poems by W. B. Yeats instead of turning it in for incineration. He follows Partridge to the Nether – a term for regions outside the city – and finds him reading the book. Seeing Preston, Partridge claims he gladly pays the price of feeling emotion. Preston executes Partridge.
Preston accidentally breaks his last vial of Prozium and is unable to refill them before the next raid. Brief episodes of emotion set in evoking memories, stirring feelings, and making him more aware of his surroundings. He intentionally skips additional doses of Prozium, hiding them behind his bathroom mirror. Partridge is replaced with an ambitious, career-conscious Brandt, who admires Preston's work as a Cleric. On a raid, they arrest Sense Offender Mary O'Brien. Preston prevents Brandt from executing O'Brien, saying she should be interrogated.
Preston feels remorse for killing Partridge, develops an emotional relationship with O'Brien, and seeks atonement. He uncovers clues that lead to meeting Jurgen, the Underground leader. Jurgen plans to disrupt Prozium production to spark an uprising and convinces Preston that Father must be assassinated. Vice-Counsel DuPont meets with Preston to reveal that there is a traitor in the upper ranks of the Clerics, and assigns Preston the task of unmasking the traitor. Relieved, Preston accepts and promises to locate the Underground's leadership.
When O'Brien is set to be executed, Preston attempts to stop the execution and fails. His memory of his wife's execution triggers an emotional breakdown. Brandt, who has been suspecting Preston of being a Sense Offender, arrests and brings him before DuPont. Preston tricks DuPont into believing that Brandt is the traitor. Preston is told that his home will be searched as a formality. He rushes home to destroy the hidden vials only to discover his son, who stopped taking Prozium after his mother died, already has.
Jurgen tells Preston to capture the resistance leaders to regain Father's trust, hoping it will get him close enough to assassinate Father. Preston is granted an exclusive audience with Father only to discover that Brandt was not arrested; it was part of a ruse to expose Preston and the Underground. DuPont reveals he is Father, having secretly replaced the original Father who died, and that his cabal doesn't take Prozium to suppress emotion. He taunts Preston, asking how it felt to betray the Underground.
Preston fights his way through an army of bodyguards to DuPont's office, confronting and killing Brandt in a katana battle. DuPont and Preston engage in a gun kata showdown. Preston wins as DuPont pleads for his life asking, "Is it really worth the price?" Paying homage to Partridge's last words, he responds, "I pay it gladly" and kills DuPont. He destroys the command center that broadcasts Father propaganda. Preston watches with satisfaction from above as the Underground destroys Prozium manufacturing plants, signaling the beginning of the revolution.
