Guy Montag is a third-generation fireman living in a futuristic version of America. Buildings in Montag's time are all fireproof, so firemen in Montag's time do not fight fires, they start them. Montag's ongoing assignment is the burning of books, which have long been banned by the government.
Montag lives in a culture where most people do not enjoy reading, the outdoors, creative thinking or interactions with other people. Instead, they seek constant entertainment, fast cars and fast living, all while consuming incredible amounts of media on giant "parlor walls" (televisions) and portable audio devices. Montag's wife, Mildred, is very much a product of this culture. Addicted to television and drugs, Mildred has little interest in conversations with her husband as he deals with life. The couple never had children, and Mildred seems to view the onscreen characters as family members.
One night, Montag meets a 17-year-old girl from his neighborhood named Clarisse McClellan. Clarisse is unlike anyone Montag has ever met; in fact her uniqueness has made her a sort of outcast from society. She has an unusual love of people and nature, and her gentle spirit, as well as her clear thinking and probing questions, gradually push Montag toward recognizing the shallowness of his life and beliefs.
Shortly after meeting Clarisse, Montag's life begins to unravel. First, Montag's wife, Mildred, attempts to kill herself by taking an overdose of sleeping pills. Then, while at work as a fireman, Montag encounters a woman who has been hiding a great amount of books. As he prepares to set fire to the banned materials, the woman chooses to be burned alive with her prized books, leaving Montag to wonder why someone would value these strange objects so much.
A week later, Montag learns that a speeding driver ran into Clarisse. She dies, and Montag sinks into a depressing dissatisfaction with life. He wonders if the answers to life and its apparent meaninglessness might be found in a stash of hidden books that he has secretly confiscated from fire sites. Montag begins to question his role as a fireman, even missing time on the job. His fire chief, Captain Beatty, comes to Montag's home to inquire about his strange behavior.
Captain Beatty explains that it's not uncommon for firemen to go through a time of searching and of wondering what answers might exist in the pages of books. He gives a long explanation on the history of how books came to be banned. According to the captain, many years ago, various groups were offended by writings that portrayed opinions contrary to their world-views. Writers gradually adjusted to a world where it was frowned upon to write anything that could offend someone. Without any controversy or conflict in the written word, most published works tended toward cookie-cutter formulas. But soon even these bland, voiceless works were considered controversial, and society decided to simply outlaw all books rather then deal with conflicting opinions. People didn't want to think anymore — they just wanted to be entertained — and so their government gave them what they wanted.
Captain Beatty gives Montag a 24-hour timeframe to study his stolen books, after which he must turn them in to the fire department to be destroyed. Montag begins an intense night of reading, but understanding the complex written language proves to be too difficult. Montag asks his wife for support, but she cannot understand why he is wasting his time reading books.
Desperate for help, Montag remembers that he once met a former English professor while visiting a local park. He debates whether it would be safe to reveal his interest in books, but he decides that the professor might be able to help him understand what he has been reading. Montag visits the professor, whose name is Faber. Faber is at first scared of having a fireman visit his home. Since he has also been hiding books, he only wants to live in secret. Once Montag explains that he has recently become interested in books, Faber decides to help the fireman. He tells Montag that the beauty and value of books lie in their detailed portraits of life. Faber explains a culture needs not only books, but also the liberty to act upon the principles contained within.
As Faber helps Montag with his reading, the two design a plan to gradually change how society views books. Faber will work with a printer to begin duplicating important volumes, and Montag will try to discredit the fire department by hiding books in the homes of firemen. The two will keep in constant communication via two-way radio earpieces.
At home, Montag encounters his wife and her friends watching television and chatting about a coming war. Angered by their superficiality, Montag takes out a book of poetry. Faber radios him to keep quiet and not reveal his new thinking, but Montag ignores him and reads a poem to the stunned group of women. Montag's wife tries to laugh off the incident, explaining that firemen often read poetry to illustrate how useless literature is. Mildred's friends are extremely upset by the poem and leave to file a complaint against Montag.
Montag returns to the fire station to turn in some if his books. In an effort to keep Montag from pursuing his new fascination, Captain Beatty begins to recite a number of contradictory quotations from once-famous books. Beatty explains that these contradictions prove that literature is dangerous, deserving of condemnation and destruction. As Beatty speaks, an alarm begins to sound, and the firemen all hurry to answer the call. They are surprised to discover that the alarm has been triggered at Montag's own home. Montag sees Mildred with her bags packed, climbing into a taxi, and he realizes that his wife has betrayed him.
Beatty commands Montag to burn down his own house. When the job is done, the captain continues to lecture Montag, and tries to have him arrested. But Montag turns the flamethrower on his captain, burning him to death. Montag then attacks the other firemen, rendering them unconscious.
As Montag flees the scene, a Mechanical Hound — a robotic machine that the fire department uses to hunt criminals — follows close behind. The machine catches up to Montag and nearly incapacitates him with a shot of powerful anesthetic to his leg. Montag fights back, destroying the Hound with the flamethrower. Montag is able to walk off the temporary paralysis in his leg, and he returns to his home and to recover another stash of books that was hidden in his backyard. He plants these books in another fireman's house, and he calls in an alarm to the fire department when he's at a safe distance.
Montag decides to visit Faber again. At Faber's house, Montag learns that a new Hound has been unleashed to find him. Police helicopters and television reporters are also in on the hunt. Faber informs Montag that he is leaving town to find an old friend. Faber says the friend used to run a printing press, and he might be able to help them with their mission to bring books back to civilization.
Montag gives Faber some money and tells him how to clean his house so that the Hound will not be able to track them. Montag then takes some of Faber's clothing and attempts to flee the city. As he runs, television stations broadcast the chase. Montag makes it to the river where he tries to hide his scent by changing into Faber's clothes. As the authorities close in, Montag jumps into the water and floats downstream for several miles until he is outside the borders of the city.
Convinced that he has evaded the authorities, Montag finds an old railroad line that he follows for several miles. He soon finds a community of like-minded intellectuals, led by a man named Granger. The renegade group welcomes him, explaining to Montag that they have memorized many great works of literature. It is their hope that can help mankind in the aftermath of the war. Montag's assignment is to memorize the Book of Ecclesiastes.
Enemy jets appear in the sky and level the city with devastating atomic bombs. Montag and his new friends pack up and begin to search for survivors so that they might build a new, better world.