Libria, a totalitarian city-state, was established by the survivors of World War III, where all emotions and emotionally stimulating objects blamed for causing the war have been forbidden. Those in violation are labelled “Sense Offenders” and are put to death. The population suppresses emotion with a daily injection of “Prozium II”. Libria is governed by the Tetragrammaton Council, led by “Father”, who communicates propaganda through giant video screens throughout the city. At the pinnacle of Librian law enforcement are the Grammaton Clerics, trained in the martial art of gun kata. Clerics frequently raid properties in the city and the “Nether” – regions outside the city – to search for and destroy illegal materials (art, literature and music) and execute the people hiding them. A resistance movement, known as the “Underground”, emerges to topple Father and the Tetragrammaton Council.
In 2072, John Preston was a high-ranking Cleric whose wife, Viviana, was executed as a Sense Offender, leaving him a single parent of his daughter and son. Following a raid, Preston notices his partner, Errol Partridge, saves a book of poems by W. B. Yeats instead of turning it in for incineration. After tracing Partridge to the Nether and finding him reading the book, Partridge explains that he gladly pays the heavy price of feeling emotions; Preston executes him as he slowly reaches for his gun.
Preston accidentally breaks his daily vial of Prozium but is unable to replace it before going on the next raid. He begins to experience brief episodes of emotion that evoke memories, stir feelings and make him more aware of his surroundings; he intentionally skips more doses of Prozium and hides them behind the mirror in his bathroom.
Partridge is replaced with career-conscious Brandt, who expresses admiration for Preston’s “uncompromising” work as a cleric. On a raid, they arrest Sense Offender Mary O’Brien. To Brandt’s surprise, Preston prevents him from executing O’Brien, saying she should be kept alive for interrogation. Brandt grows suspicious of Preston’s hesitation. As Preston feels remorse for having killed Partridge, he develops an emotional relationship with O’Brien and uncovers clues that lead to meeting Jurgen, the leader of the Underground resistance. Jurgen is planning to disrupt Prozium production to spark a populace 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. Although DuPont appears to know it is Preston, he assigns him the task of uncovering and stopping the traitor. Relieved, Preston accepts and renews a promise to locate the Underground’s leadership. O’Brien is set to be executed and Jurgen advises against interfering, as it could sabotage plans for the revolution. Unable to bear her death, Preston tries and fails to stop it. As he has an emotional breakdown in the streets, Brandt arrests him and brings him before DuPont. Preston tricks DuPont into believing that Brandt is the traitor. Following Brandt’s arrest, Preston is informed that a search of his home will take place as a formality. He rushes home to destroy the hidden vials only to find his son, who stopped taking Prozium after his mother died, already has.
Jurgen has Preston capture the leaders of the resistance to gain the government’s trust and get 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 that he is the real Father, having secretly replaced the original Father after his death, that he does not take Prozium and can feel emotions. He taunts Preston, asking how it felt to betray the Underground. Enraged, Preston fights his way through an army of bodyguards to DuPont’s office and kills Brandt in a katana battle. DuPont and Preston have a gun kata showdown; Preston wins and DuPont pleads for his life, asking, “Is it really worth the price?” Responding with Partridge’s last words, “I pay it gladly”, Preston kills DuPont. He destroys the command center that broadcasts Father propaganda. Preston watches with satisfaction as the revolution begins with the Underground’s destruction of Prozium manufacturing facilities.