When the story begins, Guy Montag is at a house fire with his colleagues. He is a "fireman"—a member of the emergency services who, in the future world of the novel, is responsible for destroying books. All books have been outlawed, and any citizen caught with them is taken away by the authorities.

After the fire, Montag cleans himself up at the fire station and heads home. It's been a perfectly typical day, and he takes his typical route, but he remarks to himself that he's been having "the most uncertain feelings" about one particular corner of his walk the past few nights. He's not sure where they came from, but on this particular night, those feelings turn out to be prescient—a young woman in a white dress is standing outside, and she introduces herself. She's Clarisse McLellan, a seventeen-year-old student, and she and her family have just moved into the house next door to Montag's.

As they chat, it becomes clear to Montag that Clarisse is an unusual young woman. She does not prefer to stay inside and watch programs on the "parlor walls"—large television-like screens that take up entire walls of a family's home. Instead, she likes to learn, listen, and observe—hiking, walking, butterfly collecting. She tells Montag how much there is to see when you move slowly and laments the speed with which most people in their world move. She asks him if it's true that firemen used to put out fires, and he dismisses the thought. "Houses have always been fireproof," he tells her.

As they say goodbye, Clarisse asks Montag if he is happy. The question seems so foreign to him that he's almost confused by it—it's never occurred to him to wonder before. As he returns home, he contemplates what the answer might be. After a short time, he is dismayed and astonished to realize that he truly isn't. He's been wearing his happiness "like a mask," and Clarisse has taken it off for him.

Montag goes up to his room, bewildered. His wife, Mildred, is in bed, watching one of her parlor wall programs on the ceiling. She's wearing "seashells"—a small pair of in-ear headphones that transmit sound from the parlor wall directly into her ear. As Montag prepares to get into his own bed, he kicks something with his foot and realizes it's an empty bottle of sleeping pills. With horror, he realizes that the bottle was full that morning—Mildred has taken them all. He calls the police.

Two men arrive with a machine to pump Mildred's stomach, and Montag is very unsettled by their cavalier behavior—as his wife is having her stomach pumped, they're smoking cigarettes and talking to each other as though this is business as usual. He asks them angrily why they sent technicians instead of doctors, and they tell him there simply aren't enough doctors to go around—they get nine or ten calls a night like this.

After they leave, Mildred begins to come around, and the color returns to her cheeks. It's two a.m., yet Montag can still hear laughter and voices from Clarisse's family's house across the lawn. Unsettled and confused after what has just transpired, he wanders to their front door. He considers knocking but decides against it, returning home to his wife.

In the morning, Mildred has no memory of what has transpired. When Montag leaves for the fire station, it's raining. He sees Clarisse again, standing outside in the rain, and she encourages him to open his mouth and taste it. He laughs and dismisses the thought. But once he's alone, for just a split second, he does.

As their friendship develops, Montag begins finding small tokens from Clarisse—flowers, chestnuts, preserved leaves. As they chat one day, he tells her warmly that she makes him feel like a father. She tells him how the education system has failed her generation—they're kept busy all the time, but they're never educated. Adults, too—sometimes she rides the subway during the day to listen to people, and they never talk to each other about anything.

Shortly thereafter, Montag stops seeing Clarisse around the neighborhood. At the station, as the radios are predicting imminent war, Montag probes Captain Beatty about the history of firemen. Beatty is surprised at the questions, but before the conversation becomes too deep, an alarm sounds, and the men rush to prepare for a burning.

When they arrive at the house, they find that the woman who lives there has not yet been taken by the authorities. She refuses to leave, and so preparations for burning begin around her. Montag finds himself hiding one book away in his armpit as the chaos ensues, and when the house is finally doused in kerosene, the woman herself produces a match. She lights it, burning herself amid her collection.

After the fire, Montag returns home. He's distraught by the woman's suicide and anxious about his hidden book, and his emotional state makes him more aware than ever of the distance between him and Mildred. He asks Mildred if she knows what happened to Clarisse, and Mildred tells him she's fairly certain Clarisse was hit by a car and killed four days ago.

The next morning, Montag wakes up feeling sick and asks Mildred to call Captain Beatty and let him know he won't be going in to the station. He asks Mildred, who has little interest in his story from the night prior, how she would feel if he quit his job. The prospect annoys her—if he wasn't prepared for the work, she says, he should have thought of that before becoming a fireman. He responds, "Was I given a choice? My grandfather and father were firemen. In my sleep, I ran after them."

Captain Beatty arrives to check on Montag, saying he knew he was going to call in sick. "Every fireman, sooner or later, hits this," he tells him. Launching into a long oration, Beatty tells Montag about the history of firemen and how books came to be illegal in the first place—the people didn't want them, he reveals. The government didn't choose this life, the citizens did.

Before leaving, he pointedly cautions Montag about the "itch" to find out what books might say. It's normal to be curious, he says, but if a fireman found himself in possession of a book, he'd probably want to return it right away before he got himself in trouble. As he leaves, he asks Montag if he'll be in later. Montag promises he will and says goodbye.

After Beatty leaves, Montag tells Mildred how unhappy and angry and heavy he feels, and confirms that the captain was right: he did steal a book from the old woman's house. He opens the air conditioning vent and shows Mildred that it's one of many books that he's taken. Mildred tries to destroy the books immediately, but Montag calms her. He wants to look at them first, he says, and he begins to read to her.