It only takes one
One of the best quotes from the movie is "People shouldn't be afraid of their government. Governments should be afraid of their people.". This seems to be something that all governments want their people to forget or give up for "security" provided by the government for the "good" of the people.
In 2027, the world is in turmoil, a virus is ravaging Europe, and the United Kingdom is ruled as a police state by the Norsefire Party. At the top is High Chancellor Adam Sutler. Anyone opposing the ideals put forward by the party are classified as "undesirables" and are imprisoned to be executed in concentration camps, sound familiar?
We have Evey Hammond walking home after curfew, she is spotted by a few of the secret police who are about to dish out their own "punishment" for this violation of the law. There is also someone else out after curfew, a vigilante in a Guy Fawkes mask named "V", he rescues Evey.
After her rescue they watch V's demolition of London's main criminal court, the Old Bailey, which is accompanied by fireworks and the "1812 Overture". Inspector Finch of Scotland Yard is ordered to investigate V's activities and the state controlled media report the demolition as "emergency measures".
V, however, interrupts the broadcast and paints a different story, he also invites everyone to meet him on next year's Guy Fawkes Night outside the Houses of Parliament. During his escape from the TV station V takes Evey to his home, where she is told she must remain for one year.
Evey manages to escape to her friend, comedian and talk show host Gordon Deitrich. It is here that we learn that Gordon owns prohibited materials, including subversive paintings, an antique Quran, and homoerotic photographs. After Gordon performs a satire of the government on his show, his home is raided and Evey is captured.
Evey is imprisoned, questioned and tortured for information about V, she finds a note written by actress Valerie Page, a former prisoner who was tortured and killed for her lesbianism. Evey is told she will be executed unless she reveals V's location. At this stage she would rather die, and informs her captures of such.
She escapes the prison only to find herself in V's home. V was the one who had "captured" her at Gordon's home, and had been torturing her in order to free her from her fears. Evey initially hates V for what he did to her, however, she realises she has become a stronger person because of it.
Finch learns V is the result of human experimentation and has been targeting the people who were involved. Finch is an investigator whom searches for the truth even against "orders" to the contrary. He traces V's past to a bioweapons program in Larkhill.
Finch learns that the deadly virus was due to the experiments undertaken at Larkhill. Finch learns that Creedy, a leader of the Norsefire Party, released the virus onto English soil, killing 100,000 British people in order to frame the outbreak as an attack from a terrorist organisation. The Party, used the ensuing wave of fear to win the election and bring in sweeping powers.
As November 5 nears, V mails Guy Fawkes masks to the population of London, the population has now begun to openly question the party's rule. On the eve of November 5, Evey returns to V, who shows her his plan for November 5. He leaves it to Evey to decide whether to enact the plan while he meets Party Leader Creedy. V had made a deal to surrender, V however, reneges on his deal and kills Creedy and his men.
Evey is found by Finch whom is now truly disillusioned by the Party's regime, Finch allows Evey to put the plan into motion. Parliament is ultimately destroyed.