Fahrenheit 451 is a speculative fiction novel written by Ray Bradbury and set in an undefined future year.

The main character, Guy Montag, is a fireman. In the dystopian world of the novel, a "fireman" is someone who burns books—in this society, all books are illegal contraband. Any citizen caught hiding them is taken away by the authorities, and the firemen burn their house down to destroy any books hidden inside.

The narrative begins late one night, as Montag is finishing up a house fire with his colleagues. He cleans himself up and heads home, noticing as he approaches his house that there's a young woman in a white dress standing nearby. She introduces herself as Clarisse McLellan, aged seventeen—her family has just moved in next door, she tells him.

As they chat, Clarisse reveals herself to be an eccentric, complex young woman. Unlike most people—who live contentedly in their rigid, structured society without asking too many questions—Clarisse is inquisitive and curious. She asks him if it's true that firemen used to put out fires instead of starting them, and Montag finds the question absurd. "Houses have always been fireproof," he assures her.

As they say goodbye, Clarisse asks Montag if he's happy. The question confuses him, as though he'd never thought to ask it before. He arrives home, contemplating the refreshing strangeness of the interaction, and finds that his wife, Mildred, has taken an entire bottle of sleeping pills.

Montag calls the authorities, and two men arrive with a machine to pump Mildred’s stomach. The technicians are very casual and cavalier as they handle Mildred's procedure, which Montag finds to be incredibly unsettling. When he asks why they didn't send doctors, they tell him there just aren't enough to keep up—they get nine or ten cases a night like this. Eventually Mildred seems rejuvenated, and she wakes the next morning with no memory of the night before.

In the coming days, Montag sees Clarisse around the neighborhood, and they begin to develop a friendship. She starts to leave him small gifts that show her appreciation of the natural environment around them—flowers, chestnuts, preserved leaves. One day, Montag tells her warmly that she makes him feel a bit like a father. As they grow closer, she reveals more of her observations about the world: that other people don't talk to each other about anything, that nobody likes to go outside, that other children are violent and scare her.

Around this time, the radio starts predicting that war is imminent. Montag has stopped seeing Clarisse around the neighborhood, but her influence on him is tangible—he's noticing things about the world that he never has before, and he is starting to wonder about why things work the way they do in society. As the firemen are called to an alarm one night, he finds the burning procedure to be more difficult than usual. He can't help his curiosity, and he steals a bible. The owner of the illicit collection, a stubborn old woman, refuses to leave the premises. As soon as the firemen douse the home in kerosene, she strikes the match herself.

Shaken by the woman's suicide and his theft, Montag returns home and begins acting strangely. He notices how wide the divide between him and Mildred has become and contemplates how little they know each other even after ten years of marriage. He asks her if she knows what happened to Clarisse. "I think she's dead," Mildred tells him.

Montag wakes up ill the next morning, refusing to go to work. Captain Beatty stops by to check on him. This is very common, he tells Montag—at some point in every young fireman's career, he experiences a moment like this. Beatty sits down beside Montag and begins to tell him the history of firemen—that the system didn't develop this way because the government wanted books burned. The people, themselves, had decided what they valued—they wanted short, quick, digestible information with few decisions to make. The firemen, in turn, developed to maintain order in accordance with what the people want. "Today, thanks to them, you can stay happy all the time," Beatty tells him.

Beatty tells Montag that it's only natural for a fireman to feel an "itch" to know what books might say, but he cautions that Montag should trust him—they say nothing. Montag promises he'll be in later, and the unspoken agreement between the two is that he'll bring the stolen book back. After he leaves, Montag reveals to Mildred that he's been hiding other books in their air conditioning system. Together, they begin to read.

Montag takes the stolen bible to show a retired English professor named Faber. Faber tells him about the world of books and what's been lost without them in the years since they were declared contraband. Montag asks Faber what they can do, and together they develop a plan to subvert the fire department by printing their own books and planting them in other firemen's houses. Faber gives him an in-ear transmitter so the two can keep in touch.

Later, Mildred's friends come to the house to watch the parlor walls together. Impatient to get back to Faber, Montag struggles to behave normally toward their guests. As the women start discussing politics, Montag becomes angry and—despite Faber's pleas in the earpiece—takes out a book to show them. Mildred lies to cover his tracks, saying each fireman is allowed to take one book home per year, but the damage is done. The women are angry and upset, and all of them leave.

Montag returns to the fire station and hands the book to a laughing Beatty, who calls him a fool and begins another lecture. Just then, the alarm rings, and the firemen prepare for a burning. When they pull up, Montag realizes in horror that it's his house they've come to burn. Beatty demands Montag take a flamethrower to the house. As he does, Montag asks Beatty if Mildred turned him in. Beatty confirms that she did and then adds, "when you're quite finished, you're under arrest."

Noticing the transmitter in Montag's ear, Beatty hits him in the head and confiscates it, threatening to trace it back to Faber. Montag shoots the flamethrower at the taunting Beatty, who is killed, before burning the rest of the crew. He flees, snatching a few hidden books from the garden as a radio alert sounds for his capture.

Montag runs to Faber's house for help, and Faber tells him there are academics and intellectuals living in secret in the woods. A lengthy chase ensues, and Montag manages to shake the authorities by following Faber's directions.

After a long hike and a cold float downstream, Montag finds a group of people sitting around a campfire. A man called Granger tells Montag they've heard the news reports, and they've been waiting for him—he's among friends now. Granger asks Montag if he has any books. Just one, Montag says, a book of Ecclesiastes, but it's only in his head. Granger tells him that's exactly where it should be—he and his colleagues have all memorized books. Someday, when it's safe, they'll write them back down again.

The men put out the fire—Montag's very first extinguishing—and begin to move downstream. As they do, a bomb goes off over the city, and the impact knocks the men down. As they stir, the dust settles, and they see that the city has been completely flattened. Granger tells Montag the story of the phoenix—a great mythical bird, who dies and is then reborn from the ashes—and the men walk toward the city together in silent contemplation.