In 2032, the world is in turmoil. The United Kingdom is ruled by the fascist Norsefire Party, under High Chancellor Adam Sutler.
On November 4, a vigilante in a Guy Fawkes mask, “V”, rescues Evey Hammond, an employee of state-run British Television Network, from members of the “Fingermen” secret police. They watch his demolition of the Old Bailey, accompanied by fireworks and the “1812 Overture”. Inspector Finch of Scotland Yard investigates V’s activities. V hijacks a BTN broadcast to claim responsibility for the destruction, encouraging the people of Britain to rise up against their government and meet him on next year’s Guy Fawkes Night outside the Houses of Parliament. The police attempt to capture V. Evey helps him escape, but is knocked unconscious.
V takes Evey to his home, where she is told she must remain for one year. V kills Lewis Prothero, Norsefire’s chief propagandist, and Anthony Lilliman, the Bishop of London. Evey offers to help, but escapes to the home of her boss, talk show host Gordon Deitrich. In return for Evey trusting him, Gordon reveals subversive paintings, an antique Quran, and homoerotic photographs. V confronts Dr. Delia Surridge, who experimented on him and other “undesirables” at Larkhill concentration camp; seeing her remorse, he kills her painlessly.
After Gordon satirizes the government on his show, his home is raided and Evey is captured. She is tortured for information about V, her only solace being a note written by Valerie Page, a prisoner tortured and killed for being lesbian. Evey is to be executed unless she reveals V’s location. When she says she would rather die, she is released, finding herself in V’s home. V captured her at Gordon’s home, staging her imprisonment to free her from her fears. The note was real, passed from Valerie to V when he was imprisoned. He informs her that Gordon was executed when the Quran was found in his home. While Evey initially hates V for what he did to her, she realizes she has become a stronger person. She leaves him, promising to return before November 5.
Reading Surridge’s journal, Finch learns V is the result of human experimentation and is targeting those who detained him. Finch searches for V’s true identity, tracing him to a bioweapons program in Larkhill. Finch meets William Rookwood, who tells him about the program. Fourteen years earlier, Sutler, Secretary of Defence at the time, launched a secret project at Larkhill which resulted in the creation of the St. Mary’s virus. Creedy, the current leader of the Norsefire Party, suggested releasing the virus onto the UK. Targeting St. Mary’s School, a tube station and a water treatment plant, the virus killed more than 100,000 people. The outbreak was blamed on a terrorist organisation. Norsefire used the wave of fear and chaos to elevate Sutler to the office of High Chancellor and win an overwhelming majority in Parliament, taking control of the country, as well as profiting off the cure for the virus. Finch discovers that Rookwood was V in disguise, and though he initially disbelieves the story, his faith in the Norsefire government is shaken.
As November 5 nears, V distributes thousands of Guy Fawkes masks, while the population questions government rule. The UK descends into anarchy, ignited when a Fingerman shoots and kills a girl painting graffiti, only to be killed in turn by enraged citizens. On the eve of November 5, Evey visits V, who shows her a train filled with ANFO explosives in the abandoned London Underground, set to destroy Parliament. He leaves it to Evey to decide whether to use it. V meets Creedy, with whom he made a deal to surrender in exchange for Sutler’s execution. After Creedy executes Sutler, V reneges on his deal, killing Creedy and his men. Mortally wounded, V tells Evey he loves her before dying.
As Evey places V’s body aboard the train, she is found by Finch. Disillusioned by the Party’s regime, Finch allows Evey to send the train off. Thousands of citizens wearing Guy Fawkes masks march toward the Houses of Parliament. As Creedy and Sutler are both dead, the military receives no orders, and allows the crowd to pass. As Parliament is destroyed, Finch asks Evey for V’s identity, to which she replies, “He was all of us.”